There is no new protocol or protocol features, so no "new mail system" around. Only a REST wrapper around the same old thing. You'll still have to support old clients on the other end. As far as I can see, it's only an enabler for email app builders. Not that's a bad thing at all.

Still I would love to see people plug other protocols in. I guess that was your point. Making everything fit in the REST paradigm is anything but progress in my humble opinion.