I've been using Rust for a bit lately, and I rather like it. However, compiling Rust is painfully slow, even for the smallish things I'm doing. Until it's very fast, I think compiling to Rust is an awful idea for Nim. Nim's quick compiler is a big benefit IMO.
I rather disagree with @Krux02; the LLVM backend (which must be what @Krux02 refers to) is developed independently by @arnetheduck and I doubt that Araq spends much time on it yet at all. However, looking at D, the LLVM backed compiler is the one that generates the fastest code, and I hope that maybe one day we'll see the same from the Nim LLVM backend. Rust is not just **advertised** better than Nim. They announced a date for Rust 1.0, and explained what it means, and they've been pretty good about holding to it and then having new releases every six weeks. That's impressive. I prefer Nim as a language, but I believe that the future for Rust looks more assured than that for Nim.