Re: Question to Google

Unfortunately, every time we've looked at the data, the conclusion has been that it would cause unwarranted user impact. IIRC the most recent blocker was a major US ISP whose clients would experience breakage if even just one NS record was dual-stacked.

There are many zones (including your isc.org) that have several name servers dual-stacked, and they didn't notice a problem. Furthermore, since the DNS is a tree, resolution of google.com requires a proper resolution of the root and .com, both having IPv6 name servers. So, this answer is at least insufficient.