I thought nudity was against the rules, yet I see the latest Izayoi Sakuya set that nil! posted is entirely nudes.

Has the no-nudity rule been repealed?

Well, I think that non-allowed nudity means pornography. Those photos of Izayoi Sakuya is more like erotic than porno.

Hrm... What exactly is the difference between erotic and pornographic nudity? It just a judgment call?

Think of it as the difference between rating:q and rating:e on danbooru I suppose, that's the best way I can describe it. Judgement call if that doesn't satisfy you.