Wonderful tech, I didn't know waifu2x (nor the other one) ; best thing is that gives a nice "hand painting" effect up close, perfect style for a game like Warhammer...

Icing on the cake, the crispiness of textures may works as well with reshade sharpening on top.
It will allow a first and very simple HD upscaling just by using the tool (Thus I don't know if it's possible to process multiple textures at once).
It may need some organization, like many folks working each with a specific portion of game textures to gain some time, because one by one in waifu is gonna be very time-consuming as well...
I'll take a try working with upscaled texture and a normal map (finally found how to extract things like textured weapons with machinima - simply read the .mif files that contains the whole item).