I will preface this by admitting my only direct experience with IMAP as a protocol was with writing a few scripts to synchronise mail and having to fix bugs in the IMAP libraries I was using.

I must be missing something obvious -- how is IMAP a push protocol? All experiences with IMAP I've had are in the form of basic request-response flows.

Also, regarding JSON floats, most languages have the ability to give you errors if you encounter a float in a JSON field that is meant to be an integer. So it really shouldn't matter at all that JSON's floats are awful. I haven't looked, but does JMAP use floats?

I don't particularly love HTTP nor JSON, but if that's the only problem with JMAP then it's such a massive improvement over IMAP that we should have started switching to it yesterday.