I really like discussion capabilities as part of stash pull requests.
Why not have something similar at any time? Image "code reviews" at any branch at any time of a stash repo. Code reviews chould allow to invite reviewers to review certain files, one branch, several branches, all branches of a repository.
On top of that admins should be enabled to define restrictions (e.g. do not allow creation of pull requests if a code review is not finished)

Suggestion for code review states:

• opened
• closed
• canceled

roles:

• initiator
• reviewer
• guest
• admin

actions:

• open (admin, initiator)
• comment (admin, initiator, reviewer maybe guest)
• cancel (admin, initiator, reviewer)
• block (admin, initiator, reviewer) - meaning no pull requests are allowed
• approve (admin, initiator, reviewer)
• read (admin, initiator, reviewer, guest)
• answer (admin, initiator, reviewer, guest)
• rate comment/answer (admin, initiator, reviewer, guest)

• create task (admin, initiator, reviewer) - could be a jira ticket/task or a stash tasks e.g. add a test for method xyz
• resolve task (admin, initiator, reviewer)
• reopen task (admin, initiator, reviewer)
• cancel task (admin, initiator, reviewer)

• creation restriction rule (admin)
• drop restriction rule (admin)

• add notification (admin, initiator, reviewer, guest)