CSS grid works in IE11 with a few restrictions. Requiring IE11+ support is quite common for websites targeting the US market at least. Unless your audience is pretty unusual it's easy to make a case for excluding older browsers than this.
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.
On my own personal projects where I have the authority to make broad declarations like "IE11 is marginal enough to be served the mobile version", that works. But try explaining that to a corporate executive. The cost-benefit analysis is not really in favor of jumping to grid for most mass-market products.
