The biggest issue is the risk that your instance may die. From what I have seen, most instances have given users some warning. But yeah, a few have just disappeared, leaving their users orphaned with no history. This keeps users feeling they need to stay on the biggest instances, putting pressure on them.

A method for allowing users to export/backup their ID and even import it to another instance would be ideal. We (admins) need a way to ensure it is the same user, a unique identifier. Otherwise, you’ll get bots importing massive comment histories onto their accounts and faking legitimacy.

I also see this as a way for mods to maintain a ban, so a user doesn’t just migrate their account to another username/instance and continue to spam or abuse readers.