I did not suggest a complete rewrite of the project. However, they could choose to only write new code in something else, and they could rewrite certain critical paths too. The bulk of the code would continue to be a liability written in C.

I agree that it would be nearly impossible to rewrite OpenSSL as-is. It would take huge amounts of funding and time. In general, people with that much funding are probably better off starting from scratch and focusing on only the most commonly used functionality, as well as designing the public interface to be more ergonomic / harder to misuse.