Sargeras...?
- - - Updated - - -
Ye we did, tho? They literally told us Garrosh would be end boss of MoP on Blizzcon prior to it's release. Grom was meant to be the end boss of WoD until last minute decision change. Sargeras is the most obvious choice for end boss of Legion as everything is pointing at it, you don't need them to state it.