[css-grid] minmax max value

Minmax would be *far* more useful if the max was always respected. Using
grid to have a max-width content area but a full-width background is
actually really hard without this feature. For a current use case I need to
use
grid-template-columns: 1fr repeat(4, minmax(20%, 250px)) 1fr;
Being able to use viewport units and percentage units as a minimum value
while specifying a pixel maximum would make so much sense. Otherwise I'll
have to make do with using a pixel minimum, which will means my fr margins
will take up no space at smaller viewports, so i'll have to add tedious
media queries.
I realize i can set a percentage value and a max-width on the content
itself and then set grid-template-columns to  1fr repeat(4, auto) 1fr but
this is far from ideal.
I've been trying a lot of different ways to achieve the same layout.
Please consider changing this.