One of the issues I've seen with using reviewboard in an open source project I'm involved with is that it is hard to know who is responsible for landing a review.
A review request typically has multiple "reviewers" specified to get feedback but when an action needs to be taken on a review (e.g., merge the review request, discard the review request, give review!) it is not clear which reviewer among the list of reviewers is on hook to do that.
I was imagining we could have a new field that can be set on a review request that identifies one of the reviewers as the main reviewer / shepherd. This will help immensely with tracking who is responsible to move the review through completion.
Has this feature or somthing similar been requested before?
This feature hasn't been requested before. It's too niche a thing to put into the core product (as different projects have different ways this works, and most companies don't do this at all). However, it's a great use case for our custom field support for extensions.
An extension can define additional fields used to collect information, such as who's responsible for landing the change, which milestone something is aimed for, or whatever else. You can read more about this at: https://www.reviewboard.org/docs/manual/2.5/extending/extensions/hooks/review-request-fields-hook/