[css-variables][css3-mediaqueries] using variables in media query expressions

I saw somebody want to use CSS Variables with media queries, like this:

   :root {
     --large: 800px;
   }

   @media screen and (max-width: var(--large)) {
     /* rules to implement some responsive design */
   }

That seems like a reasonable thing to want to do.  Can we define that 
variables in @media rules are resolved using the computed style of the 
root element?