This is a long read. Don't say I didn't warn you!
MMO design has always held a fascination for me, primarily because so many games do this so horribly wrong. The most interesting thing I like to dwell on is character development, and certain releases from S-E on FFXIV have me very hopeful that they might be the first developer that manages to do this particularly thing "mostly right".
My dream setup is one that eliminates XP and grinding 100%. While grinding, either solo, through thinly veiled grind quests (i.e. bring me 12 bear paws), or in a party can have some occasional appeal to a player, I doubt that any of us here logs on looking forward to a four hour grindathon be it in a party or just solo. Lets face it: grinding isn't "fun". While the party mechanics in FFXI made this better or worse for different players depending on their point of view, it still sucked.
FFXI was utterly genius in letting its players use one character for multiple jobs. This binds a player to the character and knits a tighter community than the throwaway alt cultures of certain other games. Not only did it make everything that your one character do more meaningful, but let you alter your play style almost at will depending on what you felt like doing or how you want to play that day (or hour, for that matter). The place where this breaks down is that each job that you take on forces you to start over at square one and repeat the exact same horrific grind that you did on previous jobs and taking you to the same xp camps for hours of mindless grinding.
How it could work:
My dream system is one that allows you to keep this job flexibility while making for meaningful character development without any experience grinding whatsoever. How could this be done? A combination of quest based skill gain, weapon/shield AP based skills, job trainers, and an open skill allocation system similar to that used in FFIX (or blue mages in FFXI, if you're familiar with that).
Imagine starting the game. You are a nothing: no job, no skills, no anything. You do your little intro cut scene stuff and at the end you are given an adventurer's coupon that you can turn in at a storyline NPC to receive an onion weapon for free (others would be sold at a cheap cost should you wish another). So, you find the guy and select an Onion Axe that has an AP skill on it  Axe. Outside of town you kill a couple crabs (c'mon, you know there will be crabs everywhere!) and in 8 kills you learned Axe skill. Yay you!
Now that you have a weapon skill learned, your job changes to that of the weapon you chose (staff might be BLM, club maybe WHM, sword RDM, knuckles MNK, etc) so you are now a warrior! NPCs in town now offer you quests based on this choice. One injured warrior might want you to kill the skeleton in his basement and offers you a shield if you kill it. The shield might have an AP skill  Defender on it. A barbarian might offer one on one combat to all comers, offering to teach Warcry to those who can best him, but charging a "teaching fee" of a farmable item to those that fail. A weapon merchant might offer to teach you a weapon skill for your axe if you bring him the broken weapons of certain beastmen that live beyond the next valley. Through this kind of organic system a character could develop many of their early skills for their job.
Once they've learned most of the basics and gone far enough in the storyline of the game they would get a quest to go to the next town. This would be akin to the starter city to Jeuno march. In this city they would meet a trainer that would teach them free of charge a couple things simply for arriving and offer other skills in return for favors. Additional NPCs would offer other skills or quest rewards that have AP learned skills as well. Most importantly, though, is a quest would be offered to teach the player how to "crosstrain" their skills. I imagine you'd probably need to go collect an apron, a worm, and a skull from somewhere or other. While at any time you could swap jobs at your house, you wouldn't be able to unlock the abilities of other jobs until this time.
Once this quest is completed, you'd be able to spend skill points on the abilities of other jobs similar to how blue mages set their spells or abilities are equipped in FFIX, except that the number of points you have to buy those skills is based on the total number of skills you have on all jobs combined (and naturally, the skills of your current job are free). So, lets say you have 30 skills learned across three jobs: this might net you 20 points to spend. You could choose to spend 10 points on White Magic 1 (Cure and Regen) and maybe 10 points on Evasion 1 from THF. Maybe you've been more adventurous and have done more jobs so you have 100 skills learned ... you might have 50 points to spend. As the number of learned skills goes up, the conversion ratio goes down, so maybe the difference between having half of all skills learned and every skill in the game learned is maybe a 5% difference in total skill points available to spend.
A setup like that described above would allow for a number of things:
1) Character customization while retaining a cohesive core of abilites so that there are recognizable jobs.
2) A grind free story driven character advancement process. Each job would have its own quest series and goals, though it would be helpful if many in each skill range took you to places frequented by those of other classes simply to encourage grouping to achieve these goals without resorting to "three mage doors".
3) AP skills would be naturally gained while doing the above quests in most circumstances and would mostly encompass weapon based actions or direct actions (like defender on a shield, etc). Most AP skill weapons would be given as quests, or the AP skill would be on multiple weapons of a weapon tier (think level 30-35 swords as a weapon tier, for example), though certain spectacular weapon skills might only be learned off of impossibly difficult to acquire weapons (relic weapons and relic weapon skills come to mind ... not gamebreaking, but an improvement for those who put in the time and effort).
4) Mage spells could be learned through quested reward scrolls, 100% dropped scrolls from certain "questline bosses" (think the rank 3 dragon, for example, who might also be a kill goal for other class quests as well), farmable scrolls for certain specialty spells (erase scroll anyone?) from special events, or from the weapons themselves as AP abilities for "tier" spells (ref. White Magic 1 being Cure/Regen, White Magic 2 being Cure2/Regen2, etc) or class defining spells such as Raise or Refresh. Bards would learn the majority of their songs from the instruments suited for them that would give bonuses to the song along with teaching it to them, these instruments being gained through similar means to mage scrolls.
5) Skills could be grouped as "ranks" so that you couldn't learn skills from a higher tier rank until a certain number of skills from your current rank are learned, and weapons and armor could require certain skill ranks to equip preventing starting players from learning Axe skill from their onion weapon and being tossed an endgame axe by a friend to trivialize content. This would also allow characters to recognize another character's development (i.e. "LF1M R4 Healer").
6) Progress toward any job (which also pushes you deeper into the story) would invariably help all jobs since your total number of learned skills and abilities enhances all jobs.
7) Some skills could be learned simply through exploration. Take sky in ffxi for example: an area such as this may have a few reclusive hermits in it willing to teach some neat high end skills for a nominal cost. This would further incentivize people to get access to this area that might not otherwise bother since they aren't interested in sky god events. A peppering of quest based skill NPCs and direct trainers could assist in pushing the playerbase to explore the world.
8) New jobs or skills could be introduced easily, and balance could be easily achieved simply by adjusting the skill point cost of a given skill/ability rather than overhauling the skill itself. For example, if it is found that everyone is taking refresh as a skill and it is trivializing content, then boost the skill point cost of it upwards dramatically so that it is a more costly sacrifice to take it as a cross-job skill rather than nerfing the spell itself and hurting the job it belongs to.
How this makes a better game:
When players are freed from the drudgery of the grind it allows them to do other events. How often do you wish you could do BCNMs, NM fights, or other game events but can't because you're stuck in a multi-hour XP party? This kind of setup would free the developers to push more things such as a less-sucky version of Dynamis, Nyzul Isle, Assaults, maybe a few large scale dungeon crawls with commonly rewpawning "boss mobs" that drop decent crafting items (think blackrock depths scale or larger from WoW if you're familiar, but not instanced) or Salvage. If the developer is freed from making massive tracts of space for the sole purpose of grinding (be it quests or just simply mobs), it frees up resources for team events.
The key to this kind of system is this would not be an afterthought, but would be mandatory: forced grind is most simply put a way to give a player something to do and stretch the amount of time they will invest in your game without consuming other content. Without that grind, you'll need content for them to participate in to stay interested. This could be done through crafting or guild mechanics.
Where do you go from here?
This kind of organic mechanic could be stretched into the "endgame" play of the game itself. My favorite example would be a linkshell would have the option to rent a guild hall for a set price a week depending on their fame. Each NM would have a certain amount of fame attached to them, and when a member (or group of members) kills said NM while that shell is equipped the LS's fame would be raised up to the fame level of that NM if it is greater than the current fame of the LS. As the LS gets more fame certain of these NMs might give temporary trophies to the LS that would be displayed in the guild hall (a crab statue for Bubbly Bernie that gives +2 water resist for 48 hours to all members or a dragon statue for Fafnir that gives +15 attack for a week, for example ... think super kupowers for how this would work). As this fame rises you will receive letters periodically from various groups requesting you to take out other NMs. [Note: FFXI examples used ahoy!]
"The Archduke of Jeuno requests you exterminate a Behemoth that has taken up residence near Qufim Isle! You will be richly rewarded for your trouble, should you eliminate this threat! (Expires in 48 hours)"
Once your LS gathers up a group of people and moves into the zone, if nobody is doing the same event a kickin' rad cut scene would play and a Behemoth would spawn claimed to your party (and non-aggro to others). Aside from drops on the mob, you would also be rewarded from a pool of items by the NPC quest giver (slightly lower tier than the rare drop items, but still desirable, and all would be R/E ... a LS might be given 2 choices that the shellholder could assign to two of those that participated, or maybe could opt out of this for rare crafting materials instead in case none of the items are useful). As the LS's fame goes up, the frequency of these requests would go up as well as the quality of NM/HNM battles they are offered.
Note: the above system would allow for non-instanced HNM play for all interested without spamming spawns, bot camping, or drama while rewarding progression of the linkshell as a whole. I loved watching other people do these fights, and I imagine others did to given the amount of low levels that would sneak from Qufim in to watch whenever they'd hear a King Behemoth fight was underway. The reward/trophy system would also allow more casual players to contribute however slightly to the progress of the whole by regaining those low level trophies from fights that the hardcore players may not have the time or inclination to do giving relative newbies an immediate place in endgame. At the same time, a limited rate of repop on these mobs and a slight scarcity of rewards to any one LS would prevent the entire server from forming one massive zerg LS. My thoughts on improved LS mechanics are here: linky. Allowing everyone to participate? What a novel concept ....
At any rate, given that development resources aren't spent on building grinds for the players, more creative things such as that could be done that would be more enjoyable and more productive for them (in the end making you subscribe longer and making S-E some bucks in the process). Further, from a development standpoint, it wouldn't be too difficult to add new event mobs to a system like that described above making game enhancements and content expansion outside of major overhauls (the assault system, salvage, etc) relatively trivial should multiple organic systems be added.
I'm sure some people would hate this type of system for various reasons. That's okay. For me it would be a dream, allowing me to do whatever the heck I wanted and always participate in a storyline or adventure rather than falling asleep between pulls (I've actually fallen asleep pulling as a merit party bard before due to the tedium of it, but that's another story altogether). What are your thoughts if something like that kind of character development was implemented?