The big issue on GitHub is that it doesn't work across forks: I can't create a PR for B that targets A, which both live in my fork, in the parent repository.
The other problem is that without extra tooling it doesn't give a good user experience. It's too easy for B and C to accidentally be merged into A, unless you mark them as WIP, but that requires manually unmarking them when A is ready. There's also no UI to easily navigate across the stack of PRs.
The other problem is that without extra tooling it doesn't give a good user experience. It's too easy for B and C to accidentally be merged into A, unless you mark them as WIP, but that requires manually unmarking them when A is ready. There's also no UI to easily navigate across the stack of PRs.