Don't look to Google to do anything in this space but continue to push their creepy ads and lock people in.
What I want to know is whether JMAP can help push end to end encrypted email for everyone. Probably not, because that's not part of FastMail's feature set.
Google are unlikely to implement JMAP for the same reason they've:
- ignored pleas to implement IMAP properly going back to its inception
- have IMAP disabled by default for new users, and for most corporate users (requiring a GSuite admin to explicitly enable IMAP if employees want to access their corporate email with a client).
Google benefit massively from people not using IMAP clients and being forced into their product UIs.
That said, I wouldn't call it dead in the water for this reason. Google's tactics here have reduced the overall usage of IMAP clients, but they also serve as strong motivation for that small niche of users to move away from Gmail.