Can't get over how good Waifu2x is with anime artwork. I wonder if it could be used to create 4k anime...Hmmmmmmmm
EDIT: If you want to know where this brief thought led to, my GPUs are currently rendering out the frames of the opening sequence of Sakura Trick at 1440p - lol
4k would take about 1.5 hours to render. Damn my PC is amazingly powerful.
EDIT2: The results of this brief experiment -
https://www.youtube.com/watch?v=17R1K887h4E
Check it out in 720p, that's the original resolution - however Waifu2x performs noise reduction, so 720p here is still better than the source video. Then check it out in 1440p - it's a massive difference.
I did a couple of frames in 4k, it's even better. It takes a lot of time, but with a GPU farm the work load can be split up. I can imagine an entire episode only taking a day to Waifu2x. Really amazing results.
Here's an image comparison of the title card display frame, taken a 720p cut-out of the middle of it;
http://imgur.com/avEZjcR
A single 8k frame took about 18 seconds to output on one GPU and it's 79% the file size of the entire original source video without audio. There's 2151 frames in this 1:29 OP. It would take around 6 hours to render this out in 8k on my PC with two GPUs and it would be about 25 Gigabytes.