We have a repository with a review gated merge policy (requires 2 reviewers to approve before merge to master is allowed). I recently branched another developers feature branch and made changes, I created a pull request so that they would get a notification that they should merge and update their branch. However... what happened was that stash then required two reviewers to approve the PR. The gated reviewer stetting is global in a repo.
Imo, it is desirable to whitelist / blacklist branches for requiring review. In my case we would whitelist 'master' as the only one requiring review. Going the other way, globs would be useful, e.g. blacklist 'feature/*' as not requiring review.