The main problem with IPv6 only is that most app developers (most
programmers totally) do not really have access to this, so no testing is
IPv6 only is easy to setup if you already have dual stack.
On my Mac it is "System Preferences", "Network Preferences",
"Advanced", "TCP/IP", "IPv4 -> Off" then reboot to clear any lingering
It's about as easy on a Linux and a *BSD box.