Consider 2 git commit sets, we'll call them 'commit set A' and 'commit set B', that are related to two features, A and B, respectively. Furthermore, let's say that feature B depends on feature A. Feature A could be an object or singleton in code, a submodule, etc that is used by feature B. Many times I find myself building up feature A and submitting a review for A and while waiting on review A to complete I fully implement feature B and submit review B.
Now we are faced with 2 reviews, seemingly independent, but heavily intertwined. Now let's say that we also have 2 reviewers, A and B again, respectively, and they start to independently review each feature. reviewer A may be taking his precious time, while reviewer B is chugging away. Reviewer B has no way of knowing that the content of his review depends on the content of another review that may be full of flaws.
I propose that links as dependencies be added that allows you to tie two reviews to each other such that when reviewer B opens his review he sees a link to review A and can see that said review is not complete. This could indicate to reviewer B not to waste his time reviewing feature B until review A is complete, otherwise he could be wasting his time reviewing a feature that my change, due to a change in feature A.
Furthermore, this could be expanded to have descriptive links (blocks, is blocked by, relates-to, etc), much like Jira's issues have links to each other.