I am quite optimistic about Rust. It combines an area that needs PL theory badly - systems programming. But does so in a very practical way. Instead of attempting to control side effects, it promotes immutable data as a default (yay!) and uses type checking to enforce data lifetime and memory safety.
As anyone who has been studying high profile bugs knows, memory flaws are a huge problem.
Mozilla is well on the way to having the most secure browser with Rust.