Here's hoping they add the elementals we've seen in Abyssea, but as it was mentioned above, with a bit more control over them. I really doubt we'd see any more controllable avatars like Carbuncle/etc. But would indeed be fun if they created Hybrid ones, for example; an avatar that's both water as well as wind based, but ofcourse would be (more than usual, due to being hybrid?) weaker against the counter-elements.

Again, would be fun, but I doubt it.