You can use what is, essentially, a totally different grid layout engine which works in IE11 only, but fortunately doesn't interfere too much with the more rece

You can use what is, essentially, a totally different grid layout engine which works in IE11 only, but fortunately doesn't interfere too much with the more recent grid spec since everything is vendor-prefixed. It is not just "a few restrictions"; you can't even get close to a grid-based layout that works in IE10/11 by accident. It's doable, but practically, it might be a fairly reasonable decision to give up on giving IE the nice layout and falling back to a flat "mobile" layout, if you're doing progressive enhancement properly.