This is a good idea.  The activity pub protocol was based on an idea like this tranlating email (specifically inbox and outbox) to http.  That is now a decentralized network used by 10m-100m users.  And there is even a bridge to nostr.  Since nostr is already a subset of http, so could do it already.  A specific version transmitted over relays could work too.  Most of the work is done there.