Anyone here remembers natural selection I and II? They were hybrid RTS/FPS where a single player would play an RTS game and other players would play units. I felt like there was something to be explored more there...
Also one thing that always created great space control were front lines: total commander has that, and capture the flag (I remember league of legends having a “dominion” mode that was really fun). I also remember an RTS where you could occupy buildings.