@alex Not yet.
But what I'm planning to do is similar to what you're doing in Ditto (if I understand it correctly).
- Client interacts with the server using Mastodon API.
- When the user performs some action, the server creates an activity and sends it to the client.
- Client signs the activity and sends it to outbox (per FEP-ae97).
So, I think implementing FEP-ef61 in Ditto may make sense.