CGNAT would also be easier on routers too, since currently they need to maintain a table of their port being used to the destination ip and port. Whereas with ipv4x, the routing information can be determined from the packet itself and no extra memory would be required
That's only true when forwarding IPv4x -> IPv4. When you're going the reverse direction and you need to forward IPv4 -> IPv4x, well, still need a table then.
