Devices that don't support IPv6, or don't have IPv6 enabled, will just share an IPV4 address in a NAT pool at the ISP level. It's not pretty but it works.
Sort of. There are some very real limitations what what how much you can NAT too.
Never mind what happens when various services break due to double NATing and the various port filtering, think VOIP and the like. Probably not terribly difficult for a few P2P programs to DoS your ISP wide NAT as well.
