I would love to see a federation model where each user has an encrypted profile and content in their own archive that they manage and/or have stored somewhere for them, which they can then use to join servers and choose what data from their profile they share with who else on that server, as well as participate in server local and federated public channels, as well as private data exchanges facilitated but not readable by the server or federated network of servers you have a user account signed up.
This sounds like more work/requirements/issues placed on the casual users, it won't work, people are too lazy. You have to lean into the 90%/9%/1% rule and let the instance admins and community moderators handle everything for the casual users.
You're right though, it doesn't need to be ActivityPub. However no one says a platform can't support multiple federation protocols at the same time, at least while a transition is ongoing.
I think user friction without federation will always result in too much lock-in. Federation is our only chance to actually defeat the network effect and allow new platforms/instances to actually have a fighting chance at competing when they are better.
It prevents the iron grip on users/content like Reddit/Twitter have achieved. Enshitification can be defeated by moving instances, which is way easier when it can be done piecemeal instead of all at once, users can move at will and not even lose their friends and communities. Lemmy.world is less than a third of the Threadiverse, and only like 1% of the Fediverse. Enshitification relies on slowly boiling the frog, but here with federation that would cause a slow bleed of users moving until there's no one left in your enshitified instance. Finding alternatives is really easy and you'll already be used to the software since there are other instances with the same software.
If the software tries to enshitify then the code can be forked, instance admins can band together to support the new fork. Or switch to a different platform entirely like PieFed instead of Lemmy. Or even just changing the frontend to Photon or something like that.
I think for maximum control it would be cool to have separate
Block communities from instance
Block posts from instance
Block comments from instance
That might be too many buttons though. Maybe hide them in your settings as separate block lists, and when you click the existing "block instance" button it just adds it to all 3 of the lists
I'm still open to Chat