In our workflows, our senior engineers are subscribed to observe all reviews for their reports. In previous (v6) versions of Collaborator, the creator could promote a subscribed observer to reviewer. This is not possible in v10 and will prevent us from upgrading to this version as it would be a major impact on our workflows.
One thought is to make everyone an admin, but this is less than ideal.
EDIT: This is already supported through settings. Admin -> General -> Subscriptions Mode : Set to Mandatory Don't Enforce Role