The devil is in the details. All applications that use the Socket interface (which is almost everything that talks on the network) still needs to be rewritten.

The devil is in the details. All applications that use the Socket interface (which is almost everything that talks on the network) still needs to be rewritten. Firewall rules still need to support longer addresses, even if you do keep the old ones--it is basically the same situation we are in now, only the line between the networks is fuzzy and there is more confusion. You still end up with two sets of configurations for everything.