@kissane The only solution for this is #NomadicIdentity (a.k.a. #AccountPortability) which #Streams and #Hubzilla have for years.
Streams is #PublicDomain, other projects can probably take the code and implement it. (I'm not saying it is easy, but at last they probably don't have to reinvent the wheel or start from scratch.)
Streams and Hubzilla are #fediverse software too.