I did some looking into this a few days ago, and I can understand the sentiment. I can't understand the proposed implementation. There is a lack of technical discourse and heavy criticism of any negative opinion. I don't want to defend big publishers, I have not bought a new AAA game in many years. I think they are user hostile.
Stop Killing Games is just way too broad. Remove online DRM checks from my single player game? Sure, I have been on board with that for a very long time. Make sure my MMO stays playable forever? You're asking for a miracle. You as a consumer need to be informed about what you're paying for. It's your job.
"Just release the server's source / binary" is a pipe-dream and I figured more people here would understand this. Modern software is super complex, distributed, entangled with external services and dependencies. Often it's not just isolated, should you be forced to release the backend serving all of your (still active) games? Has anyone considered the security implications? Should you be forced to use only libraries that you can distribute? Can you see how this may stifle creativity?
"Just state when the game will go offline" is impossible. The game will go offline when it can't be responsibly funded it anymore. Whether that's 2 or 10 years from now. If a company has to declare when your game service will expire, expect most online games to transition to a subscription model going forward. If the consumer won't have that, expect less of them to exist. It's going to backfire spectacularly. A better idea would be to mandate a minimum support window, and refunds within that window.
What constitutes a "playable state"? Is the anti-cheat in an online FPS integral to playability? Many would argue so, I'll let you think about that one. This movement is riddled with such ambiguities.