I like to point out few thing why this system doesn't work.
1. FFXIV have multiply classes on 1 character. In a general, Quests are level Based, quests open up by either a line form or by level. FFXIV can't do it because there is 19 classes and 8 of those classes are combat related. Why? For example, those who leveled a WoW character or warhammer or whatever should count the amount of quests you took to become a level 60 or even a 85. I am pretty sure you did over 100-500+.
Now that mean you have 1 character reach level 60 or level 85. However, FFXIV let you level up to 19 jobs/classes to 50. Meaning you need to either repeat them all or there are 19 times 100-500 quests.
Think of the burden for the developer.
2. Quest system doesn't work because of LEVEL specific quest. Now imagine this, you are 32 conj. You just complete the Kill XXX dodo quests. you go back to the NPC. You change to your lancer level 31. Does it mean the NPC now reset their quest so you can take it @ 31 lancer? The world is not BIG enough to have 19 NPC giving you a quest every level.
consider 1 NPC per quest for 1 whole level, FFXIV will need 19 x 50 NPC. Meaning 950 NPC! Which is not likely to happen especially the guy who type and think all those scenarios up for a quest or several quests that last 1 level long. (they can do it if it took 5 years in development like WOW!)
3. GEARS. One major problem is rewards. Considering the fact gears in this game isn't randomly general like WoW because gears are crafted (don't get me wrong here wow have craft gear but most gear are random generated with different stats_. There is a limit amount of rewards to go around, therefore quest is reward won't have enough to go around beside money.
That's all i can think of so far, feel free to discuss.