Reading through the JMAP website [0], I'm actually wondering whether whoever's behind JMAP has looked at GraphQL. There seem to be a lot of similarities (especially the "why not REST" section).
Yep. Also I think they are using it for a subset of customers. While JMAP support in Cypht is still new, so far it's working just like IMAP, but my testing is limited since I just wrote the integration :)