I wasn't a huge fan of different mounts up until recently, however when I played the XIII-2 demo and looked into that more, I thought of how they could liken these personal mounts to that monster battle system. For example, we already know that you'll be able to summon your pet chocobo to fight for you, what about having different mounts that double up as companions for different roles?
You could have a Gobbue mount that acts as a tank, a floating eye (or whatever they're called in this one) that could act as a magic nuker, different coloured chocobos could fill different roles (white chocobo=healer?).
I think it'd be pretty fun, I was skeptical before seeing it in XIII-2 but it could really work well and add a lot of character as people can personalise their companion and it's development. The only issue I see with it being that it might come into conflict with the beastmaster or whatever they're going to add in the future, but we're already getting chocobo companions so I guess they'll either have it so beastmasters can have 2 pets, or have to pick between a companion and a tamed creature.
Hell, for a mini-game they could have people's pets battle each other, being as that seems to be the rage in mmos these days *shifty-eyes*
