Not remotely the first time I'm bringing this up, but: a lot of services don't actually need federation (with all the tradeoffs and caveats that come with that), they just need a mechanism for zero-effort account/profile creation and management that doesn't rely on a third-party service.

That's the sort of thing that could plausibly be solved with a browser extension or feature. It would be nice to see more interest of developers in doing so.

If you can eliminate the whole "pick username, enter personal details, generate password, keep track in password manager, confirm e-mail address in site-specific way, have to keep updating avatars/names across sites forever" dance, then "needing an account per site" suddenly isn't a problem at all anymore...