The transition is definitely taking a long time, are there additional reasons for delaying the switch to IPv6 other than the mitigation of the problem with NAT/private networks?
It requires cooperation from perhaps fifty thousand organisations (there are 45k ASes that announce more than one prefix, and I'm guessing that there may be 5k software vendors). Some of those have orgcharts that aren't very friendly to this kind of change.
Adding to that, even clueful places may be held back by one or more vendor or provider, all of which need to have working v6 support before you yourself can deploy it.
I thought ipv4 and ipv6 addresses could be provided simultaneously (or rather, ipv6 has provisions to be mapped to/from ipv4); you just wouldn't see any real benefits until you could switch wholesale (because you'd still be limited to whatever ipv4 can do)
That is, it was my understanding that there was no real blocker to supporting it in the interim, except for the lack of any immediate benefit. Though I'm also not clear on whether supportinf both introduces any significant complexity
They can be provided simultaneously, that's the normal case.
Suppose an ISP wants to provide IPv6 besides v4. What does that ISP need? Well, first, v6 from the upstreams, that's simple, and v6-capable name servers, routers, that's simple too nowadays.
But there's more. Suppose that the ISP has some homegrown scripts connected to its monitoring or accounting, written by a ninny years ago, uncommented, and some of those assume IPv4, and noone wants to touch them.
Suppose that ISP outsources its support, and the outsourcing company promises to do the needful regarding IPv6 support but never actually does it.
Suppose that that ISP is in a country where ISPs have to answer automated requests from the police or courts, and one of the software packages involved in that has a v6-related bug. Or the ISP worries that it's poorly tested and the ISP's lawyer advises that if there are any bugs, the ISP will be criminally liable.
And so on. Enabling IPv6 may need a fair number of ducks lined up.
