If I understand correctly, users of other fediverse things like Mastodon can follow lemmy communities (and users?) but the reverse is not currently possible. Would it not make sense for lemmy users to be able to subscribe to a hashtag or user on a mastodon instance?
This grows the lemmy ecosystem by providing more content which is lacking.
I read this as a lemmy user being able to load mastodon based content into their feed which I don’t see as adding more public content. If importing masto content this could be managed via a bot perhaps.