There is a difference between world-routable and world-accessible. IPv6 is world-routable. The network firewall would decide if a device is world-accessible.
This, this, a thousand times this. You haven't experienced the joys of networking when all you need is a firewall and NOT NAT. We could even run IPsec over IPv6 and it would work for most people without hours of pain.
This, this, a billion times this.
We're past a thousand users on the Internet now. :)
Yes, but turning every layman into a network administrator is pure comedy gold waiting to happen.
Why would that be an issue. The Ap/router will just come with a default configuration that does the right thing for nearly everyone and home users won't understand it, just like with IPv4 and NAT, only it won't overload the tiny embedded processor as easily.