The reactions to this tweet should tell you all you need to know about how people are reacting to this. Honestly I'm kind of surprised that no one bought Psyonix well before now (Microsoft probably made some offers), but I guess Epic brought out the purse. Good on Psyonix, they seem like a good developer that cares about their community stuff. They don't say anything about Steam in their news post about this but I can't imagine that they'll yank RL from it or anything. If Rocket League 2 comes down the pipe, though, I can't imagine it won't be an Epic exclusive.