I can say that Yvelont won't. And it's not just for lore/story reasons, though that is reason enough, Goliath having been with him since his youth in Ishgard. In all of the other games, chocobos are depicted as being perfectly capable mounts, sturdy enough to bear fully armored cavalrymen into battle. They're even trained to fight alongside their riders - pecking, biting, kicking.. even healing. With that in mind, without a RL point of reference (because chocobos ain't ostriches) it's difficult to say what a horse could offer that a chocobo doesn't. More than that, chocobos are a staple of the series, and I think I would lose a lot of the "feel" of this being a Final Fantasy game if I regularly used some other mount. That's just me, though.
Yvelont Navarre
Parn Paparn
IC Blog for Yvelont: http://never-your-pawn.tumblr.com
OOC Blog: http://navarre-again.tumblr.com
Parn Paparn
IC Blog for Yvelont: http://never-your-pawn.tumblr.com
OOC Blog: http://navarre-again.tumblr.com