It is strange that the wifi alliance miracast site has the Microsoft Surface listed as certified as of September. Since the RT doesn't have it, I assume it is the Surface Pro? Hope it is included since this is the deal breaker feature for me personally.
You realize that WiDi is just Intel's version of wireless display right? It might be a convenience to have WiDi as a branded feature but if it is a deal breaker there other ways to send video and sound to a display wirelessly.