I get excited when I hear of something like this, but then it often turns to indifference when "terminal" UI is shoe-horning GUI elements into large grids of UTF8. There's a time and place for GUI if that is the motivation, and for anything short of that my Pine/Alpine familiarity is going to be hard to beat.

But what would be interesting is "command-line" for a modern email client. Similar in spirit to the old mh, perhaps. Concise commands for viewing folders, threads, searching, composing etc. Which integrate well with grep, xargs etc. for bulk operations.

Rather than IMAP support, the heavy lifting of sync'ing Maildir folders could be done by dovecot, with searches by mairix.