This from 6bone (IPv6 Testing Address Allocation) Phaseout [Fink, Hinden 2003]:
During 2002 more production IPv6 address prefixes had been allocated than are allocated by the 6bone at the top level. It is generally assumed that this is one reasonable indicator that planning for a 6bone phaseout should begin.
Looks like the world is slowly switching to IPv6. I wonder how log it will take to phase out IPv4?