I don't know how to link to users, but I think Ada, the admin of lemmy.blahaj.zone, recently migrated the instance to Piefed. Might be worth reaching out
Edit: found the post I was thinking of. Looks like it's not a full migration, but there might still be some relevant insight.
I'm also now remembering another instance that has done a migration recently. I think it seemed like they were able to migrate across a lot of info, but possibly not users' subscribe lists(?), I think? I don't remember specifics, but I'll update this post if I stumble across the post I'm remembering