1, http://www.theverge.com/2012/6/16/3090944/microsoft-xbox-720-kinect-2-kinect-glasses-doc-leak-rumor

......(XBox 720 has) a unified Windows 8 foundation to make it easier for application developers to build apps that target Xbox, PC, and Windows Phone.......

2, https://careers.microsoft.com/jobdetails.aspx?jid=83367
Want to help developers build amazing application for Widows 8, Windows Phone and XBOX? The Expression team.......

So apparently XBox will have a XAML stack for app development.