How would that work? Commits in different repos aren't ordered relative to one another. I suppose you could have a "don't let me merge this PR until after this other PR is merged" feature, but you could do that with a GitHub Action; it doesn't really need dedicated backend or UI support.

> How would that work?

In practical terms: I manually write a list of PRs, and maintain that list in the description of each of the PRs. Massive duplication. But it clearly shows the merge train.