When did the post that I was responding to say anything about upgrades? The comment was about greenfield projects. I reiterate my point: if in a -greenfield- project you're not building IPv6 native, you're negligent. Get up on your reading comprehension.

If there's no IPv6 support, be an engineer and -make- some: write the software that needs the support, use different vendors that don't break it just because they are actively lazy and can't be bothered to implement RFCs that are, at this point, decades old. IPv4 needs to go away yesterday.