Thanks for your idea! I think it is totally possible to implement a screensaver with the ext-session-lock protocol. I will try to explore this idea when I have time in the next few months :)
But jwz (XScreenSaver's creator and maintainer) doesn't give me much hope: https://www.jwz.org/blog/2025/07/xscreensaver-wayland-and-lo...
I adore this project on its own merits too because using the memory values in an emulated game is something that has fascinated me since Twitch Plays Pokémon integrated their Twitch display!