The existing integration works suprisingly well given the different use cases. Bettet than Masto and Peertube.

Unfortunately Mastodon not supporting group actors is the main difficulty in the integration on its end. Lemmy has hacks like auto-boosting thread posts, but kbin and peertube don't so you can't get thread posts without following the post author.

I think allowing user following (allow subscribing to user pages) and handling tags (which I'm not sure the right approach, probably can fit in whatever multicommunity feature gets developed) are the only missing things on the Lemmy side.