DNS issuess

Server discovery
anycast, multicast, DHCPv6?

Packet size
EDNS0?  root zone response size?  glue AAAA records?

DNS server reachability

Broken DNS servers
Incorrect NXDOMAIN response when "www.example.com" has only A, and AAAA query is issued
(should be empty NOERROR)

Making root DNS servers IPv6 ready
Making ccTLD/gTLD DNS services IPv6 ready