There are actually plenty of graphics solutions for USB(2). They all use low-key GPUs with not much power in the 3D department, but the ones I have tested have

There are actually plenty of graphics solutions for USB(2). They all use low-key GPUs with not much power in the 3D department, but the ones I have tested have had no problems with true 3D payloads (accelerated, not SW rendering) of the "simpler" kind such as f.e. Quake 1, and of course no problems at all with any normal desktop usage - if it's just software-framebuffer action (which covers like 95% of anything commonly "desktop/office" with the exception of fullscreen video which can stutter at higher framerates and resolutions) they are a pretty cheap and efficient choice for expanding your desktop or laptop with another screen, without giving any notable burden on the CPU for slinging data.