Agreed. I've been working on it for a long time and against successive waves of opposition. Have something that works, though it all tends to fall apart if you need to do this across platform. I think the Misskey folks accomplished this using different ids, but they were only doing a one-time migration aka "account move", so didn't need to worry too much about duplicates. We're doing account copy/clone and both the identities and all their content are available simultaneously on multiple instances. In this case they all need the same portable-id or the whole thing quickly becomes a nightmare. But for what you're doing, I would encourage you to have a look at Misskey's migration tools for inspiration.
T
