I'm looking forward to getting JMAP Calendars and JMAP Contacts done, at which point is becomes a much more compelling replacement for multiple protocols.
https://datatracker.ietf.org/group/jmap/meetings/
https://www.ietf.org/mailman/listinfo/jmap
One could potentially write JMAP as a proxy to an existing IMAP server (just like your 'imap-api') therefore the current lack of JMAP servers doesn’t really matter.
Of course, until other email servers add support for jmap, the protocol has a bit of a bootstrapping problem. Getting support from gmail + microsoft exchange would be a huge win for jmap, and in the long run email as a whole.