Sure, devices can sit behind a firewall and I highly suggest implementing a border firewall anyway, but in the long run it will be easier. Devices can still use

Sure, devices can sit behind a firewall and I highly suggest implementing a border firewall anyway, but in the long run it will be easier. Devices can still use UPnP to dynamically ask the border firewall to open up ports, and instead of having a finite number of ports because of a single IP address that is being used to NAT now each device behind the firewall could technically ask for 65535 different ports to be allowed through the firewall dynamically. Now Bobby can run his game server on port 2275 and Billy can run his game server on port 2275 both connect to the same cable modem, and each will be able to get their own traffic routed to them.