Regardless of it ends up, the headlining feature of DX11.2 is a new Direct3D feature called Tiled Resources, which exposes a limited virtual graphics memory model to apps. This prevents loose mapping between logical resource data and physical memory, and also allows the creation of large logical resources that utilize small amounts of physical memory. That's the technical description. Put another way, this will allow a game to store textures in both system RAM and graphics RAM. In real-world scenarios, this will come in handy for things like mapping out terrain in games and coding the user interface in apps.
DirectX 11.2 Exclusive To Windows 8.1
According to Microsoft, Tiled Resources will allow developers to build games with unprecedented amounts of detail. In addition, Windows 8.1 Preview includes a new set of APIs for DirectX apps to present frames with lower latency, allowing for faster response time by the UI, Microsoft says.
Though it's an incremental update, there are some major goodies in DX11.2, which makes it even more interesting that Microsoft's limiting the API to Windows 8.1 on the PC side.