I mean, a lot of this is just ideas and the dev team [1] could well say that the picture I have in my mind is not the best way/is just simply unworkable. 
But I think if the first pending item is treated as its own entity (that is, the flag is handled, a PM is sent, the reviewable is no longer pending) and a second, duplicate pending entity is created to allow for editing and resubmitting then it could then be popped in the approval queue as a ‘new’ reviewable once resubmitted. The pending item awaiting revision could be marked clearly as such on the /pending page as well to reduce confusion (is it waiting for mod approval/is it waiting for me to revise?)
(if they ever pick the feature up to work on) ↩︎