Yeah, identity is a real problem, but someone posted a proposal to solve for that that looks perfect for this sort of thing. Wish I remembered what it was called, but basically each account could attest for the others via export of encryption keys/signatures so while you has multiple ‘accounts’ there was only one identity which was pointed to in the signature blob.

The tricky part would be getting everyone (matrix, lemmy/kbin/mbin, pixel fed, and masto) to conform to a single identity standard. If one existed, I could see them implementing it, but we’re not there yet.