I'm all for variety, but making it work within the realm of believability as also important. Having a variety of breeds of chocobo for example built for endurance, jobs types, etc would be really cool. Ones with a very distinct design, and armour.

As for other forms of vehicles, attaching a chocobo or two to a carriage to 'taxi' people about would kind of be fun when I think about it. It'd definitely be new, and has already been seen in one or two cutscenes.