Is Swift on the server a good idea? I don't own (or plan to own) a Mac. Does Apple support cross-platform tooling? I honestly don't know, but given their history, my default assumption is to be skeptical.
Why would you choose this over Go or Rust? (Rust is totally sweet for server dev, and I've spun up a few Rust servers for things.)
The Swift Open Source community is quite vibrant. They're already building it on Linux + macOS. See: https://github.com/apple/swift
Edit: They also have a Platform Support page, where they discuss their goals/intentions on cross-platform: https://swift.org/about/#platform-support