This is very old news, here's an old collection of clues pointing to Sargeras and the Legion from the MOP beta, next to the fact we know Turalyon and Alleria are returning in the next expansion thanks to Metzen confirming it directly.
http://www.blizzplanet.com/blog/comm...rn-of-sargeras
It would be stupid to have ruined the chance for demon hunters all because some of their iconic abilities were cannibalized to give demon hunter fans a little bit of homage while playing rogues and warlocks over the years, indeed. If Blizzard wants to embellish and flesh out the class, they can do it. They did it to deathknights, but of course this is argued about constantly here. We really know next to nothing about demon hunters and there is tons of room to flesh them out if they want to.