On dual-stack networks, which remains the norm rather than ipv6-only so far, and usually still require IPv4 to gain access to a large part of the internet, having IPv4 optional will mean the connection may still be brought up with just IPv6. Then people will wonder what is going on and file bugs here.
We'll revisit setting IPv4 to optional after the Precise release.
On dual-stack networks, which remains the norm rather than ipv6-only so far, and usually still require IPv4 to gain access to a large part of the internet, having IPv4 optional will mean the connection may still be brought up with just IPv6. Then people will wonder what is going on and file bugs here.
We'll revisit setting IPv4 to optional after the Precise release.