Since when was there ever a plan to disable IPv4 on the Internet? Just because IPv6 is around doesn't mean that IPv4 is going to go away.
Why would we keep around a whole separate Internet? Dual stack was always only intended for the transition period.
That was always the plan for "the future". That is get everyone to IPv6 and then get rid of IPv4. IPv4's days are numbered - but the number looks really big.