On the neverending search for using c#6 features in unity I recently stumbled over a small repository.
This project allows you - with small modifications of unity - to use the Roslyn-Compiler-Platform and with it huge amounts of fancy c#5 and c#6 features in Unity.
I'm someone living on the bleeding edge
and upgraded my project to Unity 5.4b10 and have to say: it just works.