Yup, it could, but as I noted to Paul, in the cases Sean is advocating, the client and the NAT box may not be within the same span of administration, either. IE: no, you may _not_ trust the NAT op.
In today's internet, the DNS management, the routing administration, and the ADM engineer are all outside of central administration. This is analagous to the case you bring up, and yet we work well. Proxy aggregation of address space occurs, and yet the world goes on. That the NAT administration would be different from that of the flow endpoints is orthagonal to the discussion. Perhaps you mean that the client won't know where to go because the information is changed. Well, yes, that's what NAT does. Send it to an agent aware of the change, or reference that modulation, and it will come together. -a