This is really cool! I have seen quite a few people asking about Three.js myself included. It seems like a good renderer to me, I'm not sure why some people may not like it. I already like the features you've shown such as wireframe. I would also like to try different lighting effects and there seems to be a large community to provide features like that.
The regl-renderer here in jscad is pretty snappy too, but I wouldn't know how to extend it. There is also a good regl community, I should look into that.
Thanks for sharing the conversion snippet. Can you also share the code to create your 3D grid and viewer?