Stacked diffs seems like a solution to managing high WIP - but the best solution to high WIP is always to lower WIP
Absolutely everything gets easier when you lower your work in progress.
It is entirely viable to never have more than 1 or 2 open pull requests on any particular code repository, and to use continuous delivery practices to keep deploying small changes to production 1 at a time.
That's exactly how I've worked for the past decade or so.
Oh sure, many bad ideas and poor practises such as that one are quite "normal". It's not a recommendation.