I'm also anxiously awaiting the rise of IPv6, but I'm guessing that -- in a sane world -- consumer routers will still default to a stateful firewall for IPv6, thus necessitating the continued need for hole punching. :/
Hole punching will be very reliable though - each end picks a port and starts talking to the other end at roughly the same time. Once they both start talking to each other, the flow will be fine.
