djb has a lot of brilliant ideas and excellent implementations of them. But this is neither.
On the flip side this article could serve as a great example of a Nobel disease :-)
He has written relatively well-known mail and DNS servers so I would not be that dismissive about him knowing a thing or two about internet RFCs.
I think the GP is taking the AAAA record overly literally and nitpicking the implementation detail. The analogy in djb proposal is MX records which fall back to A record. I don't think he would mind AAAA records that fall back to A record either, as long as the semantics are similar.
He literally writes "people introduced new ``AAAA records'' into the DNS protocol, creating several unnecessary complications in DNS software." He says, right there, that AAAA records are an "unnecessary complication". To say that he wouldn't mind them is in direct contradiction to what he wrote.
Further down after that he writes that the "client software, intermediate computers, and server software have all been upgraded to handle the client's extended address."
But what happens where there's software that is not upgraded? IMHO, if it's sane, it would reject the packet as malformed as security precaution. Congratulations, you've now broken DNS on the ('legacy') client. So you have to make sure every possible client is upgraded before you can even consider adding records with "IPv4+" addresses.
Or you could simply have two record types (e.g., A and AAAA) and legacy clients use one and updated clients the other, and you don't have to worry about breaking what already is working (plain-IPv4).
That sounds a whole awful lot like the exact problem he hoped it would solve.
And having written a nameserver and knowing what that ecosystem looks like, he knew that. And being famously security conscious (and competent), he knew what it would look like to get all the OS vendors to parse a 32 bit A record RDATA field as IPv4, and a 128 bit one as IPv6, and any other value as invalid, 100% of the time so that you didn't accidentally create a vulnerability by truncating addresses or such. It would've been chaos.
Once again - djb is a brilliant cryptographer, an application designer and coder, and I respect him very much for his genius there.
But I maintain that his thoughts on the topic of IPv6 transition unfortunately do not share this property, and reveal that he is completely ignorant of a lot of practical factors that are at play in that context.
