I think this is neat. You may need to make this customizable for users. As a tech lead / manager, I used to have 5-15 in-flight PRs at a time. Some of them took a week to review. I can see having them all in slack possibly becoming tiring. The bottleneck is not my attention span, but my schedule.

Secondly, and this is an easily debunked point but I want to ask it nevertheless - what stops Github from building a bot to do this? How to you plan to create additional value beyond the notifications?