I'm pretty much with Carpe on this one...I've been reading this post for quite some while and throwing in random comments, but he's voiced his opposition on this way better than I could ever have. Also Solracht's idea on combining the FF:T and WoW(sorry to word it like WoW, but we both know that's exactly what it is). I mean, I really like this idea, but it's WoW and they're trying really really hard not to be a WoW clone. If advanced jobs were introduced as specializations within current jobs, I don't think they would do it in a talent tree system. Knowing SE and how they did things in FF:XI and for that matter, any of their main stream titles, they don't copy other games that are popular at the time. They make their own mold and they go with it.
Specialization within a current job the way that the Yoshi-P words not just in his current interviews, but the interviews he's done since he's taken over "command" of the dev team...is really that of Final Fantasy Tactics venue. Not to mention the majority of the team that worked on FF:XI and is currently working on FF:XIV worked in Final Fantasy Tactics. Obviously they're going to have very strong influences from those games.
Now, don't get me wrong...in my mind, the only way to appease everyone is to make a FF:T-esque way of UNLOCKING advance jobs, once they are unlocked the way to level these jobs up is to use a talent tree system. Having a baseline of abilities for all jobs, and then having the advance jobs have the talent tree's. It makes the advance jobs more powerful than baseline jobs, which was the case in any final fantasy (sorry for all those gladiator, marauder lovers out there, just the way it's always been) and allows you to customize your advance job the way you want it to be.
For instance, I get gladiator to rank 10, marauder to rank 10, and thaumaturge to rank 10 (I apologize for spelling) and now I can unlock Dark Knight (my favored class)...now that I've unlocked Dark Knight, when I level it up I get "talent points" which can be put into any of the tree's which I consider. For this particular conversation we will say Dark Knight has 3 tree's: Enfeebling, Tanking, Damage Dealing. Remember this is just for example...I always thought DRK could've been a tank if played properly lol ^^; Now, I unlock dark knight, in order to prevent over powering the advance jobs it would have to start at a higher level as to prevent getting too many talent tree points...actually talent tree points could just start with a higher level. Let's say rank 20, I don't have a diagram of how the tree's would play out, I'm just asking you to pretend along with me. Now, I want to cross spec so I'm playing a final fantasy XI style dark knight, half enfeebling and half damage dealing...you see where I'm going now? I hope so. But look, I hate the cookie cutter of paladins have to be tanks, or gladiators...so now I can respec my talent tree points to be a tank/enfeebler, changing my play style but still giving the game that overall sense of diversity that everyone is craving right now.
Now that I'm thinking of it, it shouldn't be a problem that any job could get the talent points and be able to "spec" in any way of playing. Um...Gladiator could have a talent tree spec open up at rank 20, the three specs being Spike Damage (two handed swords), Tanking (Sword and Shield), or DPS (Sword and shield with offense passive/active abilities).
Now most of the base classes we have now would have to be nerfed, and the talent tree's would be able to buff them back up again but at the cost of "I have a gladiator that can use black magic, white magic, pugilist, and archer abilities" which in my opinion should go anyways. Of course I think that the armory system should be gotten rid of, I don't like, never really did. If it's too much to get rid of, that's fine...I'm sure they could think of something, it's not my job to and I'm going to trust them (the dev team) on that one.
If I happen to find a diagram, or illustration that could better make my opinion known, then I will paste it in a new reply. If I just edit my current post it'll be lost in 5 minutes ^^;;;