[modernerd]

It depends if your use case accepts that a site can look different in older browsers. You don't have to write a fallback if people are okay with that.

If your project's stakeholders are prepared to accept that IE 10/11 users won't see the same as Chrome users (I use, “in the same way that those on mobile won't see the same as those on desktop, older browsers such as IE 10 will also see a simpler layout”), then progressively enhancing a mobile layout with CSS Grid is a fine approach.

I accept that this can't always be the case, though. But I don't consider CSS Grid a non-starter for most sites. Browser support is now good enough that I look to use it wherever possible, and try to educate people still stuck in pixel-perfect across all devices -land.