when will you turn off -all- IPv4 in your network? no snmp/aaa, no syslog, no radius, no licensed s/w keyed to a v4 address, no need to keep logs for leos' (whats the data retention law in your jurisdiction?) etc...
The same day that we stop using RS-232C point-to-point protocol devices. The day that IPv4 is turned off, is not an interesting date. What *IS* interesting is when IPv4 disappears into the woodwork and is only used inside boxes and on internal management networks. For comparison look at the z-80 CPU which powered the early desktop computers. When the IBM PC came out, people thought that the Intel 8086 would make the Z-80 obsolete. But it didn't. The Z-80 just disappeared into all sorts of electronic devices where it serves as a controller for some function, perhaps the video display or the disk drive servos. And you can still buy them. Here is a development kit in case you want to use Z-80s in new devices: <http://www.zilog.com/docs/ez80/devtools/fl0023.pdf> The same thing will happen to IPv4. In a hundred years some engineer will be surprised to discover that IPv4 is running inside residential HVAC systems, carrying messages from thermostats and temperature sensors to the heating system, the air conditioners, and the ground heat exchangers. But within 10 years, IPv4 will no longer be doing the heavy-lifting in carrying packets across the public Internet, and that is what counts for most of us. --Michael Dillon P.S. If you are in the market for a buggy whip, here is a list of manufacturers/sellers as well as some advice on choosing the whip. <http://home.comcast.net/~a-mcnibble/Links/Link1.HTML>