That said, if one of your reasons isn't 'iOS' (in which I would recommend Swift anyways), and you are instead moreso interested in learning a systems language period, I would heavily recommend diving into Rust.

The documentation/introduction book is wonderfully written and a breeze to go through. I have found the Rust team to be a wonderful group of guys that are extremely responsive on SO, IRC, etc.

HN users pcwalton and steveklabnik both have many wonderful comments in Rust threads that go into the minutiae of why it is so powerful. I had found steveklabnik's book "Rust for Rubyists" wonderful, but it is since outdated since the official Rust book has become concentration (www.rustforrubyists.com confirms this) but the book includes some 'ruby inside of rust' examples etc.

Good luck in your journey!