Imagine an expansion where (just as a random example) the goal is to go out and defeat a bad guy simply because they are a bad guy. Not because they have the ability to consume the entire planet of Azeroth. Not because they want to rule the universe.
My only complaint about Legion so far is, "So, this again eh?"
I still pine for the day we get an expansion where the fight is Alliance vs. Horde, but not PvP based.
Hell, a human invading army would be unique at this point sadly.
I mean after we save the universe (again) in this expansion, I mean how long can they keep doing this without getting into space Jedi territory (which they have done to an extent). The legion space ships in this expansion are just lol wat