@falkreon I think all of these things are really good ideas. The first two I hope we see very soon.
Unfortunately, I'm struggling to understand how we'd do the last 3 reliably in ActivityPub. I like the ideas but I don't really have a good understanding how how the protocol supports amending messages that have already federated, other than DELETE or REMOVE actions.
I might mention it the next time the AP working group convenes, though, so thanks for that