MJF: Jupiter is a user interface library for Windows and will allow developers to build immersive applications using a XAML-based approach with coming tools from Microsoft. Jupiter will allow users a choice of programming languages, namely, C#, Visual Basic and C++.
sounds like DIRECTUI.dll to me. it actually IS exposed by Windows Runtime (COM vNext).
Jupiter is aiming to provide these developers with a managed code XAML library, so that developers can access the sensors, networking and other Windows 8 elements in a way to which they're accustomed.
sounds like other Windows Runtime components (Windows.*.dll) to me, doubt if they are really part of 'Jupiter' but anyway, its part of the whole picture.
P.S. DirectUI.dll itself is 'native code', just like agcore in Silverlight.