I could almost see the whole PvP system being revamped; if there is any truth in the allowing of cross faction mounts... I don't know that there's any truth to this, so won't comment much. But now the complete hinderance is that alliance and horde are permently set to hated for each other; and to get a non-racial mount one needs exalted with the race.
This is also no small task, even without impossibility being involved, especially such as with a human getting a Wintersaber (I think it is), where one needs exalted with both Darnasus for saber riding ability, and with the trainers for elite cat out of that zone, (not to mention getting to that zone, when the Timbermaws are initially hostile to one)...
If they will allow that though, it would be well different to see an elf (well true blood elves will be introduced) ride a wolf, or an orc ride a saber
