I hacked together a 4x (via applying it twice) scale once when i was modifying Gamescope to see how it'd look but it was both very slow and i didn't like the result so i only kept the 2x one[0].

Out of curiosity i did apply it twice to the drawing i posted in my previous comment with a 4x bilinear upscale made in Krita[1]. TBH i think a dedicated 4x network would do a better job though even then, there is only so much a network can hallucinate to fill in details :-P.

[0] https://github.com/badsectoracula/gamescope/tree/neural-netw...

[1] http://runtimeterror.com/pages/iv/images/20b9558400bcf26511d...

I've been using Pi though i'm currently doing the NIH thing and making a custom one in C++ with a web-based frontend :-P.