> In my opinion Rust and Nim would make a nice team as complementary languages

I don't think so because the syntax is very different. You would have to learn two languages, and if you know Rust and you need it for safety reasons -- then why not code everything in Rust?

Nim is very practical by design. I think some practical additional security features in Nim (pre- and post conditions for instance) make more sense than interaction with Rust or Haskell. Somewhere I read that the Nim developers plan to add pure functions (like Haskell). This would be the first step in that direction.