Yeah, that's where I think there's room for developers to have some sort of legal footing.

If youre a dev and you just stop updating your game after the changes go into effect I think you might be able to make a legal argument that you are no longer using Unity to develop your game, you just don't accept the new contract and you keep everything the same under the old license. I don't know how well this would work though since I don't know how Unity has defined "use" of their engine in prior.

Amd this might be fine for a few devs, but if you are still developing or actively supporting your game things could be more difficult. You would have to make the same argument, start converting your game to another engine, and hope your game's sales from whatever version it is currently in can hold you over until then. You wouldn't be able to make any more changes to the game under Unity without accepting the new terms.