This sounds useful, but the example of the feature rows reminds me how sad it is that CSS sometimes requires adding information about the document structure to make a layout work. In this case the number of rows.
Ideally, we would have a way to align elements even when they don't share a parent. Or maybe a flex container that can have its layout mimic another flex container so the distribution in them can line up. It seems that there are a lot of heuristics and edge cases though to keep a simple DX.