How about a customizable mount feature for which the first step would be something like taming it yourself out in the world(ofc there would be limited options since models would have to be re-designed for this to work I guess).
Then have various options that you’d be able to unlock ranging from what kind of wings you’d like(and/or magical hooves/paws) to the texture of the mount itself but also if it’s a 2-seater(or maybe even 3?) or if it has vendors, transmogger or even an auctioneer.
Or if you for example really enjoy fishing the mount could offer a option to fish while mounted and have a second lure active so you’d get double the fish from one cast.
Or if you really enjoy pet battles or just collecting pets the mount would have extra seats for your favourite pets to travel with you. (for hunters your pet could maybe have it’s own seat and not just dissapear when you fly off).
If you enjoy gathering materials the mount could have extra storage bags or maybe just proudly display your favourite race or faction with flags, ribbons and other stuff.
Mounts are one of the few things you take with you from expansion to expansion so it could be carried over indefinitely.