That is a great idea! I initially built them for another project where CSS was not available but it could really push the performance. Right now, their image is cached already when they are not moving but with CSS maybe one could render initial components with threejs and then animate them further with CSS, right? Or would you build them with CSS from the very beginning?

Maybe render them as an svg or a canvas element? I'm not too familiar with drawing stuff in 2d so I'm not sure, but the character creator could probably be converted to 2D somehow while still having the hairs and shading and stuff. 3D seems like overkill if they're always flat on the screen.

Three.js renders them onto canvas elements, actually, so perhaps there is an easy way to render them onto individual canvases and overlay them? It would be interesting to see how close one could get with 2D layers to the feel of the 3D version. I guess when they are that small, it would be very hard to notice, right?