I was interested to see if any of the Rust webservers allow C linking, but a cursory examination shows that they at least aren't explicit about it in their docs, if they do. I thought it would be interesting, because I know a number of them are looking to make sure of Rust's concurrency guarantees and futures-like libraries to provide what it sounds like you want, but would possibly be easier to reason about in the case of errors.[1]

1: This of course presupposes you know, or are willing to learn, Rust. That said, given what you've explained about libuv, the total time to grok libuv's code base and the time to learn Rust may be similar, but learning Rust may pay more dividends?