I was wondering if someone can try to create a vectorization shader for retroarch based on the depixelized pixel art examples? Their list of comparisons includes SuperEagle,Super2xSal,EPX,and HQ4x,so I know making this into GLSL shader form is possible. There is even a video of SMW showing it in action. Maybe you can even get the guy who made it to quickly throw together a shader file with the algorithm.
http://research.microsoft.com/en-us/um/people/kopf/pixelart/
It would look really awesome! 
I think xBR outperforms it, actually. At the time it was presented, I don’t think it could run realtime, either, though that may have changed in the intervening 3-4 yrs. The other consideration is that the algo just may not be suitable for GPU processing, as those others are all more frequently seen in CPU filter format.
What about the closest resembling one called EPX? (can’t remember if already in RetroArch)
No EPX shader AFAIK, but I think it’s available as a CPU softfilter.
DeSmuME has EPX and EPX+ listed as scaling filters according to its wiki page,along with 5xBRZ. Gonetz recently added 6xBRZ to GLideN64,and it looks even better than 5xBRZ!
Too bad there’s not a way to reduce the impact of shaders on RetroArch for both 3D and 2D games. The 5xBR shader really struggles for me,even on SNES with Snes9x Next. If it is possible to cache any game’s graphics and sprites for better performance with shaders instead of rendering the screen every frame,that’d be a great idea. If that can work,maybe 6xBR could be possible.
Instead of using the old 5xBR, try using xbr-mlvl4-multipass. It’s much faster than the single-pass versions and detects a lot more patterns, too.