This seems to skip the idea of stacked commits plus automatic rebasing, which have been around in Gerrit and other tools for quite a while.

If you read between the lines, the underlying problem in most of the discussion is GitHub's dominance of the code hosting space coupled with it's less than ideal CI integration - which while getting better is stuck with baggage from all their past missteps and general API frailty.

That's a good point. To clarify, Gerrit itself didn't actually do merge queuing or CI gating. Its model was stacked commits: every change was rebased on top of the current tip of main before landing. That ensured a linear history but didn't solve the "Is the whole pipeline still green when we merge this?" problem.

That's why the OpenStack community built Zuul on top of Gerrit: it added a real gating system that could speculatively test multiple commits in a queue and only merge them if CI passed together. In other words, Zuul was Gerrit's version of a merge queue.