Neat, this should be a default feature on github.com/owner/repo/pulls page (especially showing at a glance the state of the PR)
Hmm.. Might just be me, but isn't that half of the job of the reviewer, to decline a PR if it isn't fixed? The one making the PR should get a notification that it is declined. Their ball.
Yes, but as noted in the post, if the pull request author misses that email notification the request goes into a purgatory. And the pull request page has not way to glance down a list and note who's on what.
This isn't an individual notification system, it's an easily-scanned list of PR states, which has quite a bit of value for many projects.