I already do this using git branched. Whenever I have features that depends on one another I create a feature branch and then stack branches on top of each other for individual feature so it's easy for the reviewer to go through the code and and also keep the PR size quite small. Also this gives me freedom to push more than one commit for each branch to fix things.

The only annoying part is that I have to keep on merging the base branch to the feature branch constantly to keep it up-to date. If Github can provide a feature to do that automatically, then that would be perfect. Other than that, I don't see any advantage on this stacked PR approach they are proposing.