Well since adding these Zandalari Warbringers, a friend and I started farming them up. Really him, since I just tag along at a safe distance (and buff kings like a champ)!
My goal was to get exalted on all the MOP reps through the little rep drops from these guys. And so far so good!
But there's no reward. Not that what I'm doing is at all 'intended' I'm sure. But since I've shown that it is 'possible' to achieve exalted before level 90, and once learned, the mounts can be used by any lvl 20+ already, why not just lower the level required to learn them to 20 (or perhaps 40)?
It doesn't take any of the 'epicness' away, as, as mentioned above, once learned any alt can use them at 20+ anyway.
I'd add that this is just in relation to the MOP rep mounts, but I suppose the same question could apply to any of the mounts that are ultimately usesable at levels much lower than the required level to learn them, which just doesn't seem to make sense.