I've also coded an AGI script for Asterisk, has IPv6 support, although this isn't 100% correct, and it would be better if it was a fastagi daemon instead of just a regular agi script that asterisk calls each time from the dial plan.
If it was a daemon ideally you would want to be able to track which DNS servers it was getting the quickest responses from and primarily favour making DNS requests to those servers first, not to mention disabling IPv6 requests if IPv6 lookups fail.
It's a work in progress I suppose, and the more I do the more ideas I come up with.
http://www.e164.org/enum2.phps
I've also coded and submitted a patch for FreePBX:
#2797 (Encrypted ENUM Lookups) - FreePBX - Trac