My suggestion to those who would like to see Swift on the BSDs is that you try to, or sponsor someone to, port it. Dario's pull linked above and @3405691582's OpenBSD port show you the way, and given the BSD lineage of already-supported platforms like Darwin and Android's Bionic libc, I don't think it will take much.
I and others are happy to answer any questions that come up in the porting effort, and I tried to help out by reviewing Dario's FreeBSD pull and pinging reviewers on some of the previously-merged OpenBSD pulls.
Swift is an open source effort and I now have a full Swift 5.5 toolchain running on my Android phone, with most of the patches required merged into the main repo. I'm sure most of you could contribute in some way to get Swift on your favorite BSD too.