This is exactly the "one language" myopia that I was arguing against. Anyone who tries to sell me on a language or programming system that asks for complete buy-in and offers no interoperability story is immediately suspect in my book.
(FWIW, I don't think the Rust guys actually sell this line, so I'm arguing against you, not them).
No one will ever invent "the last language you'll ever need." One reason for this is that different languages excel at different things. For example, Rust is not as easy to sandbox as Python, Ruby, etc. It's also not as simple to write quick scripts in.
Another reason is that you'll never convince everyone in the world to use the same language. Even if you convinced them that they should use the same language (which is impossible), there are billions of lines of code in use that is written in different languages. If you can't interoperate with them, you are a rock, you are an island.
There's nothing "modern" about the idea that "we're going to make the last language you'll ever need."