Writing a new browser engine at all is irresponsible and ridiculous. Doing it in anything other than Rust just makes it slightly more irresponsible than it already is.

I don't see how it is irresponsible or ridiculous. More browser engines is a good thing. It might be irresponsible to bet your company on it at this point, but on its own I think it is a worthy endeavor. Plus it looks like a lot of fun to work on! This is hacker news after all.