Sapling has a way to manage multiple PRs, setting the target branch of each to its parent and adding information about the stack of PRs to each PR description.
What does this look like in practice?
It seems jj supports this workflow roughly as well as Sapling. If I have five PRs open with five feature bookmarks, changing an ancestor and pushing will update all PRs simultaneously. Github's PR view notices that the heads were updated and changes which commits are included in the review set.
Sapling shares the limitations of Github's review UI: reviews still include all changes (I think). The only nice bit is Sapling automatically submitting the PRs for you and adding the descriptive info?
As a nifty workaround, it looks like sapling recommends an external tool called reviewstack.dev to properly review its stacked PRs which show incorrectly by default on GitHub. So is there much difference?