Seems like instance admins already sort of have the ability to hide communities from all, like how Reddit would hide certain subs from r/all
https://github.com/LemmyNet/lemmy/issues/2943#issuecomment-1581485335
https://github.com/LemmyNet/lemmy/pull/2055
I think it's still not in the UI yet but maybe coming soon, and 3rd party UIs/apps could implement it
I think they're mostly just a publisher now, but they've been putting out good stuff.