This really does seem like suicide. I'm not a game dev though. Is there any reason everyone won't/can't just switch to Unreal Engine? Is this a case where they overstepped or is it like reddit where the only leverage the user base has is illusory?
I can't see future projects building on unity with this "we have changed the deal and can do it again" attitude on the other hand.
So I'd put the level of customer power here as more than Reddit users but less than Dungeons & Dragons users.