We'll see. I think mass JMAP adoption is really waiting for either apple (mail.app) or google (gmail) to jump on it.

My favorite feature of JMAP is that it gives you a single, consistent API endpoint that works for native clients, webmail and programmatic clients (like, backup scripts and things like that). JMAP means you don't have to invent your own REST API for webmail. Unfortunately, gmail, yahoo mail and all the rest predate JMAP. So it doesn't really help them in the same way.

It'd be lovely to get thunderbird working with JMAP!