The only mount I ever care about in mmos is the horses. Since Chocobos pretty much take the place of horses, I don't expect to see them in game. The one exception I can think of is Sleipnir, Odin's horse from mythology, and even then, that was not a true mount. Aside from chocobos, the "mounts" have been vehicles for the most part, not animals, but I don't see many vehicles fitting in the world of Eorzea.

However, each FF has always introduced something different, and I don't see why some different mounts can't be introduced, as long as they make sense and chocobos remain the main "mascot". Since Eorzea seems largely pre-technology, a few more types of animal mounts makes sense to me.

All that being said, I would still love to see a great deal of mini-games associated with the chocobo, including raising, racing, finding stuff, etc. I understand ffxi had some things like this, but there no reason they can't make it better.