Contributions would be happily accepted but you’d need to take care with contributing assets (textures etc) because they will likely be rejected if the provenance (licence) can’t be established.
I was told by @sebavan to add to the “Asset” folder after trying to add in “Playground” so created a pull request last night. Don’t know if they went through.
Of course, contributions are always welcome, but it’s definitely a slower process since you need to check the licensing and go through review first. If you self host your assets you can see them in your PG in minutes!