Mind that some of the major content so(u)rcerers will have to adopt their Bind 4.x hacks from the last century to make their DNS respond to 4A queries instead of just timing out as they do today ;)
To be fair, this is much less of a problem now than before. Setting a preference for quad-A is now generally feasible, whereas a year ago, it involved daily teeth-gnashing and hair removal. There are a pile of things to fix, including this, and ospfv3 and core-router packet switching rates and end-user dns requests over ipv6 and stable end-user ipv6 stacks which don't bsod or panic all over the place, and so on and so forth. This is why the Japanese government is so important for the uptake of ipv6 globally: it's going to force a population of 130 million highly-wired people to use ipv6 for everyday network connectivity, which is going to 1) wring most of these problems out and 2) cause large vendor software systems to be made ipv6-aware. These are good things. Nick