Count me in on B: Quality.
I really dislike the idea of 'Quantity' .. even if it doesn't reduce the time and resources to be spent on the more developed elements, much as it's likely to anyway.
As far as I'm concerned it takes away from mounts feeling in any way special - and I'll note I've written 'as far as I'm concerned' here; 's my voice is all. But I really do think it's a damn-sight harder for something to become iconic or seem in any way special when it's just a locked, non-customisable re-skin of the same old ambulation bonus.
Meanwhile systems that let me really develop and customise things like my mount or companion character or whatever are just so much more potential for fun and being proud of the thing, and so much less vulnerable (though not wholly so) to being liable to make things tacky-looking or so chaotic as to hurt the overall aesthetic, because no matter the customisation options there's still at least something of a unifying base.
Thankfully though, it does seem the developers are angling similarly, with only a few things being open to real customisation and bonuses ala the proposed chocobo companion system. I suppose in a way, everything else just being a 're-skin of the same old ambulation bonus' does serve to make those few seem all the more special .. though it's still no excuse to flood the game with tacky, incongruous, or outright silly mount options.