Hi Henry - One way to accomplish what you have in mind is a combination of the Re-engagement plugin and a Label.
The Re-engagement plugin allows you to set up an email reminder after a specified number of days. You can link the reminder to an activity using the 'target activity' option -- you can suppress the reminder if a particular target activity is completed. However, 'viewing feedback for an assignment' cannot be set as a target activity. Instead, what you can do is create a Label right under the Assignment on the course homepage; the Label could say something like 'I have read and understood the feedback I have received for the assignment', with a manual completion checkbox next to it. You can then set the Re-engagement activity to be linked to this Label as the target activity. If a student has not checked the box next to the Label after say 14 days, they would get an email alert.
I'd be curious to hear your feedback if you try this out.