There is actually a tool[1] that will provide the right subset of polyfills to the specific browser. However, you do need to specify the list of polyfills you use in your code.
The default included polyfills tend to cover most things in my experience. I haven't had to worry about if a feature exists in IE8 or if we're polyfillng it for a while now, it's great.
[1] https://github.com/Financial-Times/polyfill-service