notmuch support is planned! It shouldn't be too hard, if an interested user were to take ownership over the feature it could probably ship in 0.2.0. Want to help?
Curious if you've looked at nmh and mu (maildir utils)? The last time I looked, it wasn't obvious that notmuch was the better option.
And also if you've looked at jmap? It's my distinct impression that the jmap effort isn't a case of nih, but rather stems from a real need of avoiding imap limitations (in idle, various levels of extension support).
One of my project ideas, for a long time, has been to figure out if dbmail might be tricked into being a decent jmap server via a graphql(like) proxy on top of postgres...
