This was announced today by Microsoft. As a video game developer i think this is really good as it means we can actually target our game GUI to use Avalon wilthout shooting ourselfs in the foot.
Of course, we don't know about performance and such for the XP platform. But to me, Avalon is a good thing in general. Considering it combines GUI and DirectX together, seems like the perfect combination for game developers. 🙂