Making it easier to stack PRs feels like entirely the wrong direction - "when you're in a hole, stop digging" - stacking is giving the people in the hole better shovels to keep digging with, instead of getting PRs flowing through more easily so that stacking is not needed so much.
"Stop digging" is not an option when working on a project that isn't entirely internal to one (sub)organization. These are not only open source projects.
Making it easier to stack PRs feels like entirely the wrong direction - "when you're in a hole, stop digging" - stacking is giving the people in the hole better shovels to keep digging with, instead of getting PRs flowing through more easily so that stacking is not needed so much.