If you're looking into building toolkits for not-too-popular languages, I feel like Erlang should be interesting, the process model sounds like a perfect match to GUI components. I've never seen anyone trying to build that, for some reason. I have a feeling GUIs with borrow checkers are hard to get right, wouldn't advise building Rust toolkits as practice.
Rust is expected to be more-commonly used, cause it better handles the large domain of C/C++ based code, as it is less error-prone, but still fast and energy-efficient, which. Linux kernel is starting to support Rust now.
Rust for instance has no overhead of garbage collection, while Erlang does garbage collection at the end of every function.
