Consider basing the grid-flow idea on top of CSS Regions

[Schepp]

The grid-flow explainer reminds me a lot of what CSS Regions (nice blogpost) were supposed to solve. My guess is that grid-flow will face the same reasons blocking it from implementation as regions did, which is that proper CSS fragmentation needs to be solid across browser engines first.

My suggestion would be to unify the grid-flow and regions concept such that we get a generic solution for all kinds of "element distribution" use cases in the future. For example we could declare two CSS Regions which each use their own CSS Grid setup, or share same setup via CSS Subgrid, or that use another kind of layout like CSS Flexbox or CSS Multicolumn.