Requiring open protocols and guaranteed interop are feasible though.

Distributing implementations of closed protocols is speech. I don't see why such restrictions would be desirable. If you don't want to play games that use closed protocols, you're under no obligation to do so.

This is an absurd stretch. The definition is already stretched too far without additional stretching.

Just add a requirement to declare for how long the online part of the game will continue to work. With the loophole of it being "infinite" if you allow community servers.

you could probably require it to be included on sale, though.