Yeah, tbh the worst vendor lock-in part of Github (edit: other than the aformentioned social aspect) is Github Releases. And Lemmy doesn’t really use them.
I think a lemmy roadmap for the next year is hard, because scope and even individual features depend on funding (for example, nlnet funds specific features).
Maybe something like Mastodon’s roadmap would be possible though (with no specific timeline)? joinmastodon.org/roadmap