Old post, but in case it's still useful, Mbin's been working great as a bridge for propagating posts between services from my experience. Lemmy can fetch posts from thread-based instances pretty well, but on other things, Mbin feels the gap, like having from what I can notice an easier time tracking Peertube, its boosts allow propagating pretty much any posts to microblogging platforms, and being able to follow users, their posts (either from threads or microblogs) get tracked automatically, no need to look for the post's link on the search field.