Anything short of chocobo mounts is going to be fail imo, it should be what it should have been in XI with chocobo raising.

Rank 20+ to start quest.
Color of chocobo could be chosen.
should be fairly quick to obtain.
Can be summoned anywhere in the open world thats not mines/caves etc.

Anything less than that is going to be lackluster and a huge letdown, this is a modern MMO, there should be a mount system.