From the conclusion:
NAT may be a good short term solution to the address depletion and scaling problems. This is because it requires very few changes and can be installed incrementally. NAT has several negative characteristics that make it inappropriate as a long term solution, and may make it inappropriate even as a short term solution. Only implementation and experimentation will determine its appropriateness.
If we rolled back the clock to 1998 or so, that’d probably be worthwhile. At this point, everything is set for IPv6, and we just need to do it.