@jupiter_rowland I'm aware of @mikedev 's work, and I hope we will be able to agree on a pure-ActivityPub nomadic identity solution. Interop with (streams) is my primary concern. Mastodon will likely be the last project to adopt nomadic identity, so I'm not particularly worried about it (although the solution must be simple enough to implement for all ActivityPub projects, including Mastodon, otherwise it won't take off).
The same can be said about other features provided by (streams) and its predecessors. Lots of good ideas there, which I hope will be eventually adopted by other projects.