Yes, this would be helpful. Would be even better if this aligns to the layout grid. You can set a layout grid within Figma, but when setting up containers with auto-layout, it is not possible to align them on the grid. Except for manually, but that’s not responsive.
Figma, adding percentages for widths would make our design files behave like true responsive layouts across any size breakpoint. I currently have 5 breakpoints with minimum widths=90% of the available size for 1, 2 and 3 column layouts and this works adaptively with set widths, but if it was percentage based the layouts would be fluidly controlled.
Adding my +1 for this. We’ve been using percentage based layouts for fluid web design for over two decades, let’s get this basic functionality into Figma.