It would be *very* nice if there was a way to specify an arbitrary system command that is ran when a review request is submitted, discarded, or deleted (preferably with the ability to specify different commands for each action).
Use case: ReviewBoard as a "gatekeeper" for QA promotion.
Consider a commonly used distributed SCM QA workflow. You have a "dev" and "QA" branch or repo for each of your projects. Users clone/pull from dev, push to QA, and changes that pass QA are pushed/merged back into dev. This way, teams are always developing against code that has passed some basic QA.
Now imagine that your QA branch has a commit hook which automatically generates a review request on behalf of the committing user. The above feature request could make it really easy to roll back discarded/deleted requests, as well as to push diffs from "Submitted" requests back into the dev repo.