My guess is nothing or very, very little. The link you posted says that those organizations will offer their content over IPv6, it does not say that they won't continue to offer their content over IPv4.
Probaly 99.9% of the worldwide network structure is not ready to move exclusvely to IPv6. Do you believe that those content providers would purposefully cut off 99.9% of their user base for a full 24 hours... as a test?
