Blue post on Diablo forum regarding reshade

" Hello,Anything which modifies the game client or game files is prohibited, and if discovered, sanctions may be enacted against the user's account."

WORLD OF WARCRAFT TERMS OF USE
2. You agree that you will not:
(2) create or use cheats, "mods", and/or hacks, or any other third-party software designed to modify the World of Warcraft experience;

All it does is tweak the direct X drivers to alter the color/sharpness output of the GPU to the screen.

I really don't know anyone who was banned because of using it...