The first version of Swift 5.0-Dev for Fedora has been built and "works". The package is
swift-lang-5.0-0.11.20181116git201dcba.fc30.x86_64.rpm and swift-lang-runtime-5.0-0.11.20181116git201dcba.fc30.x86_64.rpm. I've tested these on a Rawhide Docker image (Podman, actually, on a SilverBlue laptop), and they compile Swift programs, but the REPL fails with:
error: Could not construct an expression context for the REPL
So clearly there's some more stuff to be done.