I want the ability to login to any given Lemmy instance with another instance's account. Kind of like how I can login to various sites using a Google account. I think it would be fantastic if I could login to say, Beehaw.org with my Programming.dev account. That way if I'm perusing Beehaw.org directly I don't have to worry about having my own account there or finding that community back at Programming.dev (and waiting for the subscription to update); I can just login with an existing Lemmy account from some other instance.

If a Lemmy instance is already federating with an instance where I have an account I don't see any reason why this would cause content/moderation problems.