Here's the current situation inside the AirPort Extreme base station:
James, As you are looking to get this to work in a wireless mode have you looked over the draft-madanapalli-ipv6-periodic-rtr-advts document by the Networking Group? In addition to all the reasons why the authors of the Local Address Protection (formerly NAP) document this document explains some of the considerations that using NAT deceases battery life due to the regular need to check if the end node is still attached. These 30 second keep alives tend to reduce battery life up to 50%.
To Paraphrase Alex Lightman:When a mobile device has a private address, it receives an endless series of "keep alives". The carrier's NAT wants to assign the private number to another device, and so it keeps "checking the roast", but this burns up the battery. With an IPv6 address once the connection is made there is no need to keep "checking the roast" every few seconds. - http://www.usipv6.com/6sense/2004/oct/october03.htm This seems worth keeping NAT out of IPv6 for mobile devices alone in addition to the reasons that were in our document.
Eric