I was drawing a diagram to understand the CSS Display transformations after the F2F resolutions and how a hypothetical ruby-root could fit in there.

I noticed that it's not clear how run-in flow-root should blockify, and you didn't discuss this in the F2F.

It was resolved that inline flow-root blockifies to block flow because inline flow-root is syntactically equivalent to inline-block, and inline-block must blockify to block because of backwards compatibility.

A run-in flow-root is basically an inline-block with some special tree munging. So it could make sense to let run-in flow-root be consistent with inline-block and also blockify to block flow.

The other possibility would be to keep it simple and only change the outer display type, i.e. blockify to block flow-root.

In practice, the difference should not matter much because I expect blockifications to trigger becoming a formatting context. But it will affect getComputedStyle, of course.

I don't have a strong opinion, but maybe I prefer consistency with inline flow-root.