I've been thinking about doing something like this. Compress images down to half resolution, then train a neural network to blow it back up and guess the pixels as accurately as possible.
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.
I did something very much like this years ago (upscaling used to be an obsession of mine). The results were pretty disappointing.
But there's a lot of space to explore there in terms of choosing and designing the neural net, choosing the right training set, and figuring out an initial transform for data that is input to the neural net.
