It was a PR it's closed and the proposal didn't went through but reading the PR it seems the use case could be done with other existing NIPs. Also for nips to be accepted they need to be implemented in at least one client and relay I think.
Discussion
I later found it on GH, PR#457 to be specific. They were actually tackling more in the context of moderation. Of course this would be an optional feature to enable or not by clients or relays.