NVIDIA are easily the ones holding it back at this point. Both AMD and Intel have OpenCL 2.0 support on windows, and Nvidia hasn't even shipped support for OpenCL 1.2. Nvidia obviously want OpenCL to die off and CUDA to do well.
Yeah, considering the terrible quality of YIFY's movie rips I wouldn't see this as being competitive with legal alternatives at all. All the audio is low bitrate stereo, and the 1080p video never goes above 2500 kbps. The second there is any motion the entire thing falls apart into a blocky mess.
Such low bitrates do make it easy to stream, but I don't think the site is correct in saying you are watching "the best quality".
There has been a neural network scaler called NNEDI3 available as a plugin for avisynth for a few years. It was trained in exactly the way you are talking about and does an amazing job at both deinterlacing and upscaling video.
It does a great job of scaling pixel art too. I'm kinda surprised it hasn't been implemented in any emulator. With the newer opencl implantation it is finally able to run in real-time.