Is there a GitHub repository for these assets, or would it be possible to make one? I would potentially like to re-do some of the potentially commercially-unsafe textures and replace them with more generic equivalents. If there's a github repository somewhere I think it would be much easier to have people contribute models and textures.

There is not, but go for it, if that's something you wanna do! I can always throw a link to it and give you credit on the page if you want