Eredar joined the Legion, somehow I do not think they would be welcome in the Alliance. They would be Horde.
Perhaps they should just reskin all the races, just making them another color like purple and call them something obvious.
Pants would be easy enough to ignore I think (see; Mechangnomes) but mounts would be an issue. If players were willing to forgo traditional grounded mounts for something that just made them go fast as a mount (a bit like Running Wild) it’d sort half the issue, but they’d still be stuck for flying mounts unless they cop a giant floating water bubble or something.