It's too soon to rely on CSS Grid. A lot of people don't (and sometimes can't) use a browser that's less than four months old. Can I Use estimates ~44% of users don't use a browser that supports the current syntax [0]. IE11 will never support the current CSS Grid syntax but does support Flexbox (with some bugs). Edge will support the current CSS Grid syntax but doesn't yet. Older phones and tablets won't support CSS Grid.
It's soon depending on your requirements, but Shoelace is forward thinking and will only become more useful and relevant as CSS Grid adoption rises. As for Edge, it's 100% as of 16.
If you're developing sites for circumstances where you can control what browser clients use, fine. Very few sites developing in that situation.
Edge 16 hasn't been released yet.
I look forward to CSS Grid being widely available and in the meantime degrading gracefully in non-supporting browsers is often viable. My concern is for the users of sites developed by the many people who do not give any thought to how their site performs using anything other than what they personally use.
Chrome, Firefox, and Safari added support for the current CSS Grid syntax in March 2017. CSS Variable support is older. Chrome and Safari have supported CSS Variables since March 2016, Firefox since July 2014. Edge only added support (with bugs) this year and of course IE11 will never support them. Older devices that can't upgrade to iOS 10 or later, like the iPhone 4S, can use CSS Variables.
[0] http://caniuse.com/#feat=css-grid