In fact, you don’t need to be based on Lemmy’s codebase in order to be compatible with Lemmy. See: Kbin/Mbin, https://azorius.net, https://narwhal.city (which seems to be lotide’s flagship?), or heck, Mastodon (although the interoperability UX there isn’t the best)

Of all the misplaced priorities by the dev team I really think this is one of the biggest. If they just fixed authorized fetch Lemmy would almost certainly be the goto host for groups among the broader Fediverse.