Good question, and I've not thought about it previously other than that we would remove content if the original artist requested us to do so. Though, we don't have a formal list of DNP content, we just expect that users post content they're permitted to or that is already otherwise shared on other sites (like e621).

I'm not against a DNP list, but I think I'd lean more towards respecting an existing DNP like https://e621.net/wiki_pages/85. Though, if we did end up getting to the point of having a lot of DNPs that don't appear on their list, we'd probably move to making our own.

I'll bring this up to the rest of the team too for feedback!