FYI: WordPress, on my view and what is happening, they supported new custom post type beside post and pages, you can turn on "portfolio" and "testimonial" for your site in Jetpack and it will appear under your WP-Calypso.

It seems that in future, we can use custom action (maybe) to register our post type to Jetpack setting, and we can decide if we want to turn on that post type on Calypso or not.

There's more and more feature is being tested for the big evolution of WordPress, version 5.0 I think!