On a more technical front, we're told the PDK supports the Linux standard SDL (Simple DirectMedia Layer) to ease in porting and development (Unreal for Linux runs using SDL, for instance), and that developers could even build apps like an audio processor that rely on PDK components but don't show up in the UI at all, or OpenGL-empowered things that aren't necessarily games or in 3D.
Also, existing developers have only been able to do "full screen" games that rely on PDK components alone, but the PDK beta lets you mix and match webOS UI with PDK elements.