Current chips like the Hummingbird will already do 1080P with one 1 GHz core, a dedicated SIMD unit and a very powerful GPU. If just playing video is the most important, use a low-power ARM core with a PowerVR VXD380, or a VXE380 if you want encoding too. Both do 1080P.
Well this will be much better suited to multitasking, especially for all the upcoming productivity tablets. Running HD video is cool, running it with a browser and Office apps in the background is better.