@oblomov yeah that’s basically all bluesky’s lists are, from what i can tell. i think for public shareable lists, it needs to be opt-in not opt-out. Too easy to be used for harassment otherwise.
block lists work similarly. as do labels. i believe people can request to be taken off, but that’s up to whoever manages the list.
moderation services would be quite a bit more complicated, idk about that. one instinctual thought i had was to be able to follow another server’s moderation decisions on an account level, but thinking about it for an extra few seconds, that’d get real hairy real quick. but maybe we could take some ideas there? i don’t know.