Something I was hopeful for but seems to have died is lemmyBB. A phpBB-style front-end to Lemmy. I'd like the accessibility of being able to use an existing account that federation brings but the forum-style approach that phpBB has.
Mostly though I've been disappointed in the teens and twenty-somethings. They seem to have, in distressingly large numbers, just opted to go along with whatever they're encouraged to use by large platform holders. There doesn't seem to be an appetite to create communities and define spaces that they control. Perhaps that's just me getting old though...
Being designed around persistent topics rather than the ephemeral post model and more visible user customisation (more prominent avatars, signatures, that sort of thing).