Both Go and Rust fit into the same niche you mentioned (statically typed, single binary, no "legacy silliness"). Both currently support the server use case better as they have more libraries and stronger concurrency primitives available. Neither has the disadvantage of poor Linux support.

While I can understand why an iOS developer might spring for using Swift for server development, I'm not sure why any backend engineer would choose Swift. There are a myriad of better choices, including those that you ruled out.