You're right that there are areas like torrenting where big tech can't really go for fear of legal consequences, but there's also the cat-and-mouse game played by IP holders against, say, torrent trackers, which leads me to think that
> open models that can use whatever data they like but must operate in the shadows without access to much compute for training
sounds pretty analogous to private trackers, where high-quality stuff is available but not in full public view. If rightsholders and big tech, abetted by states, crack down on open models I think you're right that the open source community will continue to train on liberated content, but it's not going to be as open and free-flowing as things are now. Going back to the compute problem, I can imagine analogues of private trackers where contributors, not wanting to expose themselves to whatever the law-firm letter/ISP strike analogue will be in this space, use invite-only closed networks to pool compute resources for training on encumbered content.