silverpill@nomad now has inbox and can receive activities from other servers. Outbox forwarding was also implemented. I have successfully sent messages from FEP-ae97 client to users on Pleroma and Mastodon servers.
I think this proves that full data portability is possible with ActivityPub, and that it can be implemented in a backward compatible way.
All ０７６萌ＳＮＳ content and data are available under the