Imagine if some company offered a $5/month service that connects to o365/gmail/yahoo via imap, and then presents your email via jmap. After a few years of that company making money, I could see at least one of the big 3 offering a $1/month option to cut out the middleman. And if more of them start offering the same, then it's only a matter of time before one of them offers up jmap for free.

Unlikely, but seems plausible to me.