BlizzPlanet makes a point that it could be cross-faction gameplay, given the two mounts are both spectral and one is Horde while the other is Alliance. While cross-faction gameplay is a long-requested feature, it's gotten a lot more attention lately with Real ID raiding.
Another point being made is that the mounts are new and that they could be new downloadable content or the return of the Recruit-A-Friend bonus.
Either way, quite interesting. We'll all have to keep our eyes out.