I think that AO3 should take a copyright case all the way to the Supreme Court. Mainly because I would laugh so hard when this SCOTUS slammed them down so hard in favor of family values and traditional interests, that would be fucking hilarious day. There is a reason AO3 has suddenly got a lot less combative over stripping creators of their copyrights lately, it is because they know they would lose hard. Creators should have the right to decide whether they want fanfic or not allowed, and if someone creates fanfic then the copyright should remain with the original property creator. And SCOTUS believes that too, as AO3 knows.