The hole punching is so much simpler because you don't need to guess your own address and port - you just know it
Doesn't that assume that your machine is given its own world-routable (and unfiltered) v6 address?
That's how it works in ipv6. If your network doesn't give you an address, it's broken. We do not assume unfiltered since we are talking about hole punching.
How will it get rid of TURN? Can't IPv6 addresses still be firewalled by your carrier like they do already for IPv4?