Company-chocobo glamours. I don't mean bardings, though.

There have been instances in the game lore where it's implied that the magic techniques used to perform glamours can be also performed on living things. The heretic guy in Coerthas who "turned into" a dragon is a prime example. Another example is the levequests in Mor Dhona where some voidsent (the flying eyeball ones) were disguising themselves as voidsend that have been around in the area for awhile, almost seeming native. (I think they're called hapalits?)

So, I think it would be cool to make my chocobo (when summoned for fighting) look like something else. No stat changes. No new abilities. It would just be a vanity thing.

No, I don't think SE will never add such a feature. But wishful thinking can still be fun to think about.