Isn't this also what container queries solve better? I guess maybe you want to be sure that the whole grid remains consistent instead of relying on individual containers possibly making their own decisions. So many new features to investigate, so little time :) https://codepen.io/web-dot-dev/pen/rNrbPQw

Container queries don't solve the responsive to sibling sizes issue that grid/flex can solve. And frustratingly container queries force your container element to be a new stacking context, unlike flex/grid.

I am sad that using containers and subgrids together doesn't work. Being able to query the size of the subgrid from a child element would be super powerful.