The demons and fel have been a huge part of wow lore and gameplay since warcraft 3. And many people have enjoyed the game becuse of them. But I think we can all agree that they have played their part now. And they got an awesome ending with their leader stabbing the planet in his final act before being imprisoned.
And yes at this point im pretty tired of Argus and all the demon corrupted places in Broken Isles. Don't get me wrong tho: I still enjoy the game I just think it's time for something new.
I pray for BFA to be released sooner than later. In fact I still have some small hopes Blizzard will surprise us when we least expect it!