C#/XAML SDK was rearchitected to pave the way for an upcoming C++/XAML release (more on that later).
Another WACK (certification kit) issue was fixed in the WinJS release.
As usual you can get the XAML SDK via this unlisted nuget link.
And HTML/JS SDK can be downloaded from the Download section of the client area.
We appreciate all of your feedback for these betas! Please direct it to firstname.lastname@example.org