UD is the only currently community driven alternative. I hope they deliver on what they promised.
Is this referring to artists opting-out (i.e. requesting to have their work removed) from the datasets used to create SD models? Because if so, I fully support that. In fact, I think artists should have to explicitly opt-in to their work being used in ML models. You don't get to violate someone's license terms and then point to an opt-out form to absolve yourself of liability, regardless of how good your intentions are or being a crowd-funded venture unconnected to any corporations with armies of lawyers.
ML models also appear to be more fair-use respecting than some human artists, who blatantly trace artwork. The ML model does not have the physical space to trace the works it's trained on.
As far as I can tell from a quick Wayback Machine test, that only seems to have appeared in the last fortnight[1]. None of the existing models could have been trained under the license.
[1] https://www.artstation.com/tos has it as section 46 "Artificial Intelligence" mentioning the "NoAI" tag. But https://web.archive.org/web/20221214082018/https://www.artst... has neither.