Lightroom: Add 10-bit support for end-to-end 10-bit workflow. That is, Application->Driver->Graphics Card->Monitor for true 10-bit color. At the moment, all that's missing is the application. CS5 supports 10-bit color, why not Lightroom?
On Mac: Lightroom has always uses the 16-bit math throughout in the develop module (with ProPhotoRGB as the internal working color space). With the GPU acceleration, it requires at least Lr 6.2 and later.
On Windows: It also uses the same 16-bit ProPhotoRGB math for internal image renders. But the result image data of the final monitor color transform (for display) is currently limited to 8-bit.