The progressive enhancement approach you describe does not address cases where an alternative should be provided for less capable browsers.

The closest analog in existing tools might be YepNope - "a conditional loader for your polyfills." http://yepnopejs.com/

There's an argument to be made that this is unnecessarily reducing maintainability and increasing development complexity by building redundant functionality to account for edge cases, but there are scenarios where it's appropriate. Building modern web apps with a support gradient more inclusive than latest Webkit/Gecko will appreciate the tools.