We haven't built it yet, but its on the roadmap
I'm having a hard time seeing it. My experiments with CSS animation have always performed much better in CSS than JS (again, excluding it being pure webgl/canvas JS).
And ofc there's the nice bonus that it works if I haven't chosen to trust and whitelist their website for JS yet.
The gallery has been updated with more models. Compare the same model in PolyCSS vs. Three.js:
https://polycss.com/gallery/?model=205023689 (13 fps)
https://threejs.org/examples/#webgl_animation_skinning_morph (60 fps)
It could also be helpful in scenarios where JS is restricted - emails? iframes? bulleting board user content? Dunno. Trying to come up with some that aren't just "nemo was running umatrix and doesn't trust your site just yet"
Of course that the animations won't map to all the animations you can manage with js.