Running authoratative zone for example.com with the NS for the A records on an IPv4 accessable NS but having the AAAA records for the same zone running on a different NS accessable via IPv6 - is this possible - viable - sensible?
It's certainly possible to do this on the server side - just have different versions of the zone files (aka "split horizon DNS") on the two sets of servers, with one only containing
However you shouldn't actually do it, particularly if the intent is to direct different users based on the IP protocol used in their DNS queries.
The reasons for this are several:
You're not going to be able to do this since there is no way of delegating based on request type. What you could do is delegate a subdomain and return A records for one set of nameservers and AAAA records for a different set of nameservers. However, what would happen in a dual stack environment? You can't know whether a request would prefer IPv4 or IPv6 and it's probably going to be requesting both types of records - especially in a public environment where it usually won't be the end-client which is making the DNS lookups to your server.
You could also do something similar with routing, so that you route IPv4 and IPv6 traffic to different nameservers. You'd have exactly the same problem though.