You mean in the display pipeline? No, it doesn't...if you mean in the image file, no, any file that is 8, 10, 12, 14 or 16 bit is internally processed as a ProPhoto RGB color in a linear gamma. The output in export can be 8 or 16 bit.
In respect of 10 bit display pipeline this is very relevant question.
Windows 7 in Aero Basic mode supports 10 bit workflow and assume that Windows 8 as well. Performance of desktops and laptops is constantly improving. Compliant GPUs are available and more reasonable priced monitors with 10 bits color are in or coming to market.
Many LR users are enthusiastic photographers and keen to improve performance of their systems. It is difficult to understand why new LR4 does not support 10 bit workflow. Particularly so when Photoshop has been, to my understanding, supporting it since CS5 i.e. more than two years.
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