Invite codes would be amazing! Ie, put a code into amethyst and it sets them up for the friens relay instead of dumping them in the global dumpster fire.
Not sure about being able to prevent leakage, as some have said "paywalls only work once" rings true, (also given that nostr is easy to make your own client and you can harvest notes pretty easily no matter how much wrapping happens).
Pointing notes back to their origin relay is nice, I think we already can do that with hints..?
A lot of this stuff, just needs AUTH to be a complete solution using strfry relays. I've been meaning to pony up a bounty for this..