As a very satisfied PostSharp user, I am very interested in this ! The lack of some extended meta-mechanism for creating "code contracts" that are lightweight in terms of code footprint, appear as "attributes/annotations" (using that term in the sense of C#'s Attributes), and design-time readable ... is, imho, a significant omission in C#'s evolution, and a logical extension of C#s strongly-compiled "ethos." I will definitely be testing this new initiative.
«The mind is not a vessel to be filled but a fire to be kindled» Plutarch