[zadikian]

That's a legit concern. If that's not interesting enough to the kind of user that wants all-new v6, instead start from today where some users are on the new v6 network, and say they added the 4:: prefix as a way to pick up the kind of user that doesn't want to change much. They'd still be compatible eventually. Though the reason I was thinking 4:: from the start would've been attractive enough is, a lot of people did use 6to4 and other halfway measures despite having no immediate gain.

Today's DNS6 DHCP6 etc are totally incompatible with v4. 4:: buys backwards-compatibility. Each can be updated to support longer addrs without caring whether you use it with v4 or v6.