So a few months ago I actually found a tool for this! The tool makes it easy to manage stacked reviews on GitHub. It's working super well for me. I also showed it to a bunch of people I work with, and a lot of them have taken it up.

Link: https://github.com/ezyang/ghstack

If you're interested, I'm happy to talk you through it - just book some time here: https://calendly.com/ericyu3/15min