As far as i know, there is no other side of Azeroth, it has always just been pure speculation. There are only two main threat before we face the Void Lords, which is Sargeras and N'zoth. We are most likely going to Argus at the last patch of Legion as is hinted by some of the story quests, also, where better to finish of Kil'jaeden?. Then an Expansion with Azshara as mid tier and N'zoth as end boss, then we deal with Sargeras and finally Void Lords.