Ask HN: Where is JMAP (jmap.io) implemented or being implemented?

JMAP (jmap.io), originally developed by Fastmail, got standardized more than two and a half years ago, but the Wikipedia article [1] lists only Apache James as having "experimental" support (the quotes are from Wikipedia), Cyrus IMAP server (which I presume Fastmail uses), and Ltt.rs, which is a proof of concept Android client that supports JMAP.

Where are the initiatives from the large email platforms like Gmail, Outlook365, Yahoo, Apple, and others? Where are the initiatives from open source clients like Mozilla Thunderbird? I see an old tracking bug [2] for Thunderbird, but there doesn't seem to be much progress on it (that Thunderbird has also been going through a core re-architecture and redesign with "web technologies" is another matter).

Email continues to be one of the most (if not the most) critical piece in today's connected world. I see a "chicken and egg" problem with email providers and email client software with respect to JMAP.

I've already seen IMAP support disappear from (i.e., disabled in) some providers used in the enterprise market (especially Outlook365). Are we going to be pushed deeper to use proprietary apps with no interoperability (and with fewer freedoms), like a Gmail app (while Gmail keeps scaring Gmail users who continue to use IMAP), an Outlook app, a Yahoo Mail app, and so on? One outlier so far seems to be Apple's mail clients that still support IMAP and Apple's iCloud that also supports IMAP.

I get that alternatives for old technologies take a long time to become widespread, but I can't help feeling a bit disappointed with the pace of progress.

I'm sure the folks from Fastmail may likely chime in here, but I'd also like to hear from others who are working in this space or are tracking this space.

[1]: https://en.wikipedia.org/wiki/JSON_Meta_Application_Protocol

[2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1322991