Why own sha-3 implementation?

The project is using **internal/sha3** which is derived from **golang.org/x/crypto/sha3**.
As I understand the main reason is [some fundamental issues](https://github.com/cloudflare/circl/issues/5#issuecomment-484192883) (and some optimizations/improvements).
However if so is it possible to contribute improved sha3 code to the golang std lib and use it instead own implementation?