So I found my own solution to this problem in the end.
After searching through Microsoft documentation I managed to find a new IE11 only style msTextCombineHorizontal
In my test, I check for IE10 styles and if they are a positive match, then I check for the IE11 only style. If I find it, then it's IE11+, if I don't, then it's IE10.
Code Example: Detect IE10 and IE11 by CSS Capability Testing (JSFiddle)
I will update the code example with more styles when I discover them.
NOTE: This will almost certainly identify IE12 and IE13 as "IE11", as those styles will probably carry forward. I will add further tests as new versions roll out, and hopefully be able to rely again on Modernizr.
I'm using this test for fallback behavior. The fallback behavior is just less glamorous styling, it doesn't have reduced functionality.