You can't have a full round robin of duplication. In order to have duplicates, you have to have one central original, of which all the rest are duplicates.

And that's exactly the sort of thing the fediverse is intended to avoid.

Every instance is federated but ultimately separate. The accounts on those separate instances are necessarily also separate. There is no possible scheme by which those necessarily separate accounts can be consolidated that does not involve, at some point, some central authority to implement it and/or manage it.