Pandaria will be irrelevant after WoD launch. Making everyone grind a day on every alt just to ride a bunch of mounts is silly, especially when that rep grind is no longer important.
It's exactly the kind of thing that account-wide mounts changed, and why everyone was so happy about acocunt wide mounts. If Blizzard is gonna keep adding mounts that just defy that, why even have account-wide mounts at all?
but WoD hasn't launched yet and OP is asking for it to be changed now, making your point irrelevant.
MoP reps are still current now, so you should still have to farm rep for them if you want the rewards.