https://web.archive.org/web/20160528234959/https://wiki.freebsd.org/IPv6Only discusses a FreeBSD image that supported only IPv6, not IPv4. That page is no longer live, though (hence my archive link), and I can't find anything more recent about this. My question: is it possible today, on any modern UNIX or Linux system, to support only IPv6 and not IPv4, just like that old FreeBSD image did? It's okay if the way to do this requires a custom kernel or similar work.
Other places I've seen this asked (all dated after I originally asked this question):