It would be beneficial to have the option to set submission type on an assignment to "Peer Review", so that completing a specific peer review, a set of reviews, a number of reviews etc. is the actual assignment.
The current "solution" is to create a separate assignment with instructions to complete a peer review. Then the teacher have to track if the student have completed the review when grading. This is not a troublesome task if you don't have too many students, but this is quite tedious with a course of several hundred students.