Just leave it blank for now. It'll work fine - IPv4 DNS servers will respond with AAAA records if available.
There aren't any public v6 DNS servers I'm aware of.
Yesterday I have experimented with IPv6 on my 2 kimsufi servers, and I have created an IPv6 infrastructure with ipv6 nameservers and mailservers
Everything works greate except this:
Everytime I change (in windows 2008 r2) ipv6 settings it asks me to provide an ipv6 dns server, I cannot use localhost for this, because they don't cache dns (for security).
for IPv4 OVH provides a dns server, is this also true for ipv6?
if yes, what is the IP then?