Phil,
There are ways to do that now (and have been for years) using "hidden masters"; each DA system would create it's own DNS but wouldn't be listed with DNS or with your registry as a nameserver.
Your two (or more listed servers) would work as slaves; you need some kind of program running in the background for them to pick up information from the hidden masters and rebuild their conf file so they know what to slave.
Information has been available and in the bind documentation for years and in the O'Reilly DNS and Bind book at least as far back as the 3rd Edition.
Perhaps by some kind of cosmic coincidence, I had dinner last night with a programmer who's going to work with me on building the scripts to get the information from hidden masters on Cobalt RaQs, on Plesk-based systems, on DA-based systems, and on H-Sphare-based systems (that's all we have between us).
If you or anyone else who reads this wants to help and has other brands of hosting platforms and can help us with how to get the information from them, please let us know.
The eventual scripts will be available from me on my website and will be covered under some kind of open-source or BSD license; we haven't decided yet. Either way you'll be able to use it, modify it, sell it, whatever. The BSD license is strictly less restrictive; if you modify code based on the BSD license you don't have to put the modified code back into open source.
Jeff
