Also, a meta-reply would be: whatever clever solution you think you've invented was surely considered. It's 30 years ago so memory fades but all this was discussed at great lengths on mailing lists and in meetings by people who knew what they were doing. The only things I don't think were envisioned at the time were: NAT prolonging the V4 space exhaustion significantly, and the level of inertia for vendors implementing support for V6. I was still working on that in 2005 -- more than 10 years later.