My Theory (and this is only a theory) is that the expansion after MoP will greatly feature Alleria and Turalyon and Sargeras.
I've seen way to many "subtle" hints about the return of Sargeras, who is probably still fuming that Azeroth was the only world (that we know of) that he wasn't able to consume once he set his mind to it. So I think he still has a role to play and will probably be "The Ultimate" Boss Fight but I think the hint on the tip loading screen just might suggest that Alleria and Turalyon will play a significant roll in making sure this doesn't happen, and I think they will also hail the end of Garrosh Hellscream's Warchief Role. I have a feeling that Garrosh will cause the end of the Alliance leader Varian and Alleria and Turalyon will have to play a role to ensure a strong Alliance Leader takes over and get revenge on Garrosh. An alternate to this is Garrosh decides to give Sylvannas a "Final" Death for her betrayal in Northrend and Alleria's hatred of Orcs and her love of family will force her to exact revenge on Garrosh. Either way I see Garrosh going away and Valerian too.
The Lore is too rich to say for sure, but my gut tells me that these are VERY strong possibilities. Does anyone else have any thoughts on this?