Yeah, even setting aside the impact and implication on the AI-tech-driven stock market of such a mandate, I don't think it's technically doable to implement either. What if you modified/wrote your own inference engine which uses a somehow slightly modified version of model weights, how would you want to detect (at a firmware level) that compute to be an "unsigned" model over, I don't know, a video game?

Open-weight models, at an absolute minimum the ones that already exist, are here to stay, and will continue ([0]) to get drastically cheaper to run.

[0] I shall continue to reference one my favorite articles in recent months: https://jyn.dev/tokens-too-cheap-to-meter/