I have more faith in JMAP's eventual success than you do, but I do agree that it's frustratingly slow. We knew that adoption would be frustrating slow of course, but I do hope that in 3 years' time we'll have a much better story than we have had in the three years since initial standardisation of the core and mail parts.

Certainly once calendars and contacts are done, and hopefully tasks as well, that will make a more complete ecosystem that is even more attractive than just the email component!