I don't think it makes sense to design a language by picking the closest existing suitable language and adding one major innovation. You want to do the minimal

I don't think it makes sense to design a language by picking the closest existing suitable language and adding one major innovation. You want to do the minimal innovation necessary to achieve your goals --- no more, no less. Rust designers did consciously try to minimize innovation. To that end, Rust error handling is linguistically parsimonious: the standard library Result type used idiomatically, plus the ? operator (itself very simple). To the extent it innovated, it did so by excluding dynamic exception throw/catch and dedicated error result syntax from the language. Rust async/await is also not unnecessarily innovative. At heart it is the same as async/await in JS and C#. Getting it to work with the Rust ownership model was hard and did require some innovation. LWT was dropped from Rust because it was not compatible with Rust's goals. Likewise, higher-kinded types aren't especially innovative but will require significant work to flesh out for Rust because of the ownership system.