Either use a CC0 set like Wikimedia/Flickr and throw in some dead artists like Brueghel, or train on data from a country we don’t respect the IP of. Lots of Taobao product photos out there. It’s enough.
As of about a week ago this tech runs on consumer GPUs. The weights have been downloaded 100s of thousands of times, and fine-tuning / modifying is possible.
Training from scratch is about $500k still, but it will only get cheaper and easier.
But I would not be surprised if this was trainable on a commercial GPU at home within that time. But I think another important trend that we are seeing is that you don't need to train these models from scratch.
Open-source "foundation models" means that you can usually get away with the much easier task of fine-tuning, as to not throw away / re-learn everything that these large models have already fit.
Edit: I initially said 2-5 years, but on more reflection this does seem optimistic (for training from scratch).
I don't know enough about diffusion models but if LLMs (of current size) have to use only public domain, they will be undertrained and we will see significant degradation in performance. Not to mention that Codex will be effectively dead.
You can also require cloud providers to enforce a ban on training (and deploying) such models, it's doable. Good luck training it in your basement, it will probably take you a decade.
If this is banned, it will become a lot like piracy - yes, it's available, no, most people (at least in the West) don't do it, practically no businesses do it.