Is there a public stat on how many non-WP.com WordPress sites actually use (regurlay, not just install/connect once) Calypso? Based on my experience with friends and clients it's got to be trivially low.

Calypso is cool for WP.com but it's near useless outside that for the same reasons (plugins, custom fields, custom post types).

We need a Calypso alternative that treats customization as a first class feature. That means "just works" with the existing code base, not "well you can now write a bunch of code to support a tiny minority of users".

Gutenberg (which I think is an awesome exploration, but currently 0.3.0 entirely unusable for real use) should learn from this.