We have a self-hosted site using X-theme that we want to move to be hosted on Wordpress.com Business (where you can upload your own themes etc.)
They do now state at Wordpress.com that Cornerstone is incompatible (https://wordpress.com/support/moving-from-self-hosted-wordpress-to-wordpress-com/)
We are happy to upgrade to PRO theme instead, but can you confirm that PRO theme will work on Wordpress.com ?