If only it was that simple. The two schemes are basically incompatible. In order to switch to IPv6, everyone on the Internet has to switch at the same time.
IPv6 was designed by a committee. It's a nice setup, but the committee failed to take into account any implementation procedures. They just designed it and then dropped it on the floor.
Even if everyone agreed to switch on the same day there are thousands and thousands of devices that are too old to support IPv6. There are probably millions of devices that officially support IPv6 but implement it incorrectly, something that you won't know until you actually bring it up with IPv6 addresses.
IPv6 was designed to be compatible to IPv4.