There are a lot of people I follow who moved to Mastodon, that now appear to have moved to Bluesky (I’m seeing posts on there from people I know used to post on Mastodon).
I’m not sure why. If I move over it’ll be because everybody else is there. At the moment I’m not using it much.
I don’t think automatic crossposting is a good idea. However some way to “boost” Mastodon posts onto Lemmy would be good. Mbin has a way of boosting but can’t assign a magazine. Something like that may work though. Mastodon can already boost Lemmy posts.