The current plan is to have this remain as a preview while we get feedback. We may roll some of that feedback into API updates and release them via NuGet, still as preview. The final version of the API will come in the next version of Windows. There are a number of technical reasons why that's the case. For example, the requirement of having to pick an architecture instead of AnyCPU is not something we'd want in the final API, but it's a necessity on Windows 8.1. Another is that we want this to be the API to use going forward, desktop, WinRT, etc., but cannot make it available for desktop in Windows 8.1.
That said, we want the preview to be as useful and stable as possible.
So please, use the API, build and list some cool apps, and be sure to put your feedback in the pro audio forums on MSDN.