No it wouldn't. Sadly most people don't seem to understand that IE8 and IE9 and even IE10 do not support CSS3 selectors/ or some of them. And to top it off, they also don't understand that IE is still the most popular web browser there is when you add IE8 and IE9 together.

And really anything that can be done using CSS3 selectors can be done by thinking ahead on the development and providing proper classes/ids/wrappers/elements.

When learning about CSS people typically don't choose to specifically learn what isn't in IE n

I might be a bad example, but when I see a "not supported in IE" mention and there's no pollyfill, the feature goes to the same bucket as the cool Dart features and the fun things you can do in the next version of ecmascript. Good to hear they exist, but I'll properly learn them when I'll be able to use them.