> The motivation was to avoid "merge skew," where changes appear compatible when reviewed in isolation but break once merged into an updated main.

My opinion is that this situation of a merge skew happens rarely enough not to be a major problem. And personally, I think instead of the merge queues described in the article, it would be overall more beneficial to invest in tooling to automatically revert broken commits in your main branch. Merging the PR into a temporary branch and running tests is a good thing, but it is overly strict to require your main branch to be fast forwarded. You can generally set a time limit of one day or so: as long as tests pass when merging the PR onto a main branch less than one day old, you can just merge it.

> it is overly strict to require your main branch to be fast forwarded

But merge queues (talking in general, IDK about the mergify.com product specifically) don't require fast-forwarding as far as the developer is aware. In the simplest case it looks like merging (non-fast-forward) to a temporary branch, then only updating the main branch after tests pass. This is very similar to your auto-revert except the main branch is never broken, so no wasted developer time and confusion when they pull a bad commit to start their PR.

IMHO it is a real shame that all CI doesn't work like this. It should be the default. Just this basic delay and auto-revert is already a nice boost to developer productivity. Not to mention that blocking a merge in the original PR is much less confusing than reverting and requiring a fresh PR to make the change. It adds basically no complexity other than the fact that our tools aren't set up to work this way by default which ends up requiring extra tools which are not as well integrated.

On top of this you can add batching which can be incredibly useful when your CI is slow (including things like deploying to a staging environment and letting it soak for a few hours) which isn't feasible to do per-PR even for fairly small teams.