以后?在可以预测的将来中不存在这个“以后”和“说不定”
Go ahead, do some searching and you'll find Dark Shikari already attempted to (and even Avail Media, I believe) port something as simple as the SAD function to the GPU, and it performed miserably compared to the CPU version because of how difficult it is to optimize for a GPU.
Yes, the idea of using a GPU is good for encoding. You basically have a massively parallel processor to work with, but it's so difficult to code for that no one is pursuing it. Plus, the commercial implementations that do exist absolutely suck both speed and quality wise. x264 is easily as fast and better quality than the commercial apps, so there's no point in trying them (they're all baseline I believe)