At this point, I think just having Chocobos available will please me more than anything else I can imagine, for the most part. Besides, there's so many things you can do to customize and play around with the Chocobo that you don't even need to brainstorm over other mounts.

I can't imagine convincing the player base that Roegadyn's will be able to ride a dodos, or a Lalafell's being able to mount a Drake and cruise the desert. It just sounds silly, given the art style and tone set in the world for all its creatures. That's not to say I wouldn't want to see other mounts available somewhere down the road AFTER Chocobos get their time in.

I can imagine mounting a Garlean vehicle of some sort down the road, as the story progresses. Seeing as the have technology to move around the world unnoticed and swiftly, I can see everything fitting together nicely for another possible machine-based mount, not including airships, but motor-bike type of vehicle (I.E. FF VII).

But getting back to Chocobos... You can have different sizes, color, and features (Beak, Tail Feathers, Legs, Wings) and gear/armor to equip on your bird for protection/looks to give yourself a sense of uniqueness compared to other players. These things can be crafted, bought or earned as a reward for your mount and for yourself. I rather herd goats, dodos, and sheep as a Shepherd rather than riding them. Everything has a place and meaning in Eorzea, and this is how I see it happening.