I think you will find that there are no plans to switch off IP4 at all in any co-ordinated way - there is no real need or benefit to doing so, nearly all hardware supports both, as well as a few other protocols, and there is no problem with IP4, as most locations have NAT of some kind and with that we can allow massive re-use of the number spaces.

Mike

EDIT

PS about 5 years ago MIT sold off about half its public facing adresses to Amazon The price of IP4 adresses has if anything fallen, not risen since then, so there is no obvious shortage.

A few (well, quite a few) years ago we seemed to be running out of IPv4 addresses (since they where only 4 bytes = 32 bits long), and IPv6 seemed like a very urgent solution. But other techniques - like network address translation (NAT) that can put many device behind  single public IP address have avoided the original problem, or at least delayed it for long enough that the immediate problem feels to have gone away. I doubt the mobile sector will be able to abandon IPv4 ahead of the rest of the internet.

    - Andy.

I also believe the IPV6 adoption on the internet has been slow, meaning that there is still need for IPV6 to IPV4 NAT to access internet content