I like most of the suggestions going on. Maybe not Bacon Mage... too oily for me. But it occurred to me that maybe we're missing the mark on our theories.
SE has stated that they are changing the game play so that we won't "level up" simply by grinding out monsters. I read one of the interviews on the ZAM Wiki site for it, and they are pushing for weapons to be the keystone of growth. This leads me to believe that each character will start off without a "job" and will end up earning them based on what skills they use the most. Such as, say, using an axe will increase your strength. Where as using a club or staff would increase your ability to use magic.
That being said, maybe each class will be limited to what weapons they can use, and will have to specialize by using certain weapons / schools of magic.
The only thing that I am concerned about is making a system of specialization and then still being flexible enough to switch jobs. The thing I admired about FFXI the most was that the job system was surprisingly flexible. You can change your job just by visiting your Mog House. I hate to compare MMOs, but in games like WoW, you were stuck with one character staying one job. In FFXI, if you find a rare item that would be perfect for your other job, then you can change jobs after you get it. For example, the Soboro Sukehiro fight goes a lot smoother if you have a couple BLMs around to stun the mob. But it is such a large event that most people who go want a swing at getting the sword. In a game without such a flexible job system, it would be difficult to get a mage class to go to an event that benefited one specific melee job.
As far as what jobs I want to see in the game, I really want to have more viable tank classes. One thing that is far too common in MMOs is an over abundance of Damage Dealing classes, and a shortage of healers and tanks. I was thinking if they made most of the melee jobs have some form of threat control and a way to lessen damage, (particularly for a game that allows for solo capabilities), it wouldn't go unappreciated for tough situations, but it would also allow for more utility in a group. In this way, you could make certain jobs specialize in more defense, and others in offense, so that traditional roles could be sustained, but also have more leeway in getting a quick group for relatively simple goals. That way, end game content is preserved for each job to fulfill their natural role, but every day minor challenges don't take hours to accomplish.
A change I would enjoy seeing is less consumables. I did not enjoy classes that were based on using items continuously. For example, Ninja was a class that seemed to be noted for two abilities; Dual Wielding and Shadows. Many other jobs would seek Ninja as a subjob because it allowed for more mistakes with less risk. Unfortunately, particularly for melee DD, it was crippling to other subjob choices that would allow for more damage output. It seemed to me that it became over used for most situations. It became a "go-to" answer, and I would love to see more strategy than to simply throw shadows at whatever new obstacle we're met with. I'd really like to see SE address that issue. To stop picking on Ninjas, jobs such as Ranger and Corsair were also very item-based. I understand that for "reality's sake," when they shoot an arrow, it's gone. But it made leveling the classes that much more expensive, on top of how difficult it was to make decent money. (Not quite as hard once you had a higher level job.) But it still deterred from time that could be spent better playing the game than farming the same drops for money. I don't see any reason, other than to consume time, (not something the casual player wants to do), that SE couldn't implement a system similar to FFXII with the ammo selection, in that you simply choose what type of ammo you wish to use. /end rant.
I'd like to see some more exotic weapons. Keep the basics. Swords, axes, daggers, and the like. But what about something along the lines of a whip? Or maybe even more artistic weapons, like a fan or spiked poi? No one else thinks that'd be cool? Add in some elemental weapon buffs... Have a fan that shoots fire when you wave it. Maybe get a different form of dancer when you skill up?
I'm just tired of seeing everyone running around with the same weapons. Whenever an expansion came out with new jobs, I was hoping that they'd add more weapons / weapon skills. They proved that they could do it with Katanas and Great Katanas. So I was disappointed that they decided against doing it again.
The only thing I really don't want to see is anything similar to Dark Cloud. (For anyone who has played it, you know what I'm talking about.) I really don't want to continuously repair and upgrade your weapon by customizing it. I'm just hoping SE steers clear of that type of upgrade system.
We all know that there will be a default healer, default tank, and probably a few melee/ranged/magic Damage Dealers. I am just hoping for jobs that are both deeply rooted in the Final Fantasy series, and inventive in their own rights.
Short Answer: Beastmaster Pride!