Address allocated but not live
If all these people and companies are refusing to move to IP6 after so many years of pushing it, you have got say there is soming very wrong with it. The basic IPv6 model makes the is wrong assumption we want everything on the internet. We ( low level, part time and amateur network support folk) want to stay with what we know, and there are many more of us than ISPs and backbone peering super egg heads.
We are fine with IPs and Internet peers using IPv6, if you keep on the dirty side of the firewall. We want none of it inside our companies and homes. We are happy with or 10 and 172 addresses. We have are comfortable with NAT, OSPF, Vlans and tags. We DO NOT WANT an internet for every device. I do NOT want my LED light bulbs or my garage door on the internet, because I can not protect them. It is hard enough to keep the PCs safe. I can patch the PC, but not the coffee distributer, or the toilet water pump.
So make it easy to keep IP4v inside, and you can use whatever you want outside.
It simply is not true the IPv4 addresses have run out. They are allocated, but much are not actually used on the internet.You can check this yourself using ping. Pick some random addresses, and ping. Yes some people block at the firewall, but most companies do not as it is really hard to debug your internet connection if you do.
Monthly charges for each IPv4 address.
You will get lots of scrappy bits returned. So like was done for phone numbers, you need to weaken the link between the number and routing. Another layer of mapping is required, But on the firewall or the dirty side of the firewall. Plus if you are billing individual addresses, you can fine / block addresses used for DDOS / spam / scam. You would encourage encrypting on everything - firewall to firewall - so everything is signed - end to end - and harder to snoop / spoof.