This is shameless self-promotion, but part of a working theory I have that Mastodon users have more to offer Lemmy than your average Reddit user. See my other post about it here: https://lemmy.blahaj.zone/post/2174573
TLDR: Mastodon users are inherently active posters and already understand federation. Also there are MILLIONS of them.
Please consider following if you’d like to get more Lemmy in your Mastodon feed or more Mastodon users in your Lemmy feed!
Last I heard Lemmy devs are explicitly against this. Mastodon users can still make top level posts over here but I don’t think that’s what you had in mind.