If the protocol sucks, it'll go mostly unadopted.
See also: xhtml and arguably ipv6
I'll bite. While xhtml can be ignored rather safely, IPv6 not so much. IPv6 adoption is like the Y2K problem, but with no clear cut off date. We know we will run out of IPv4 addresses, but when depends on who you speak to or what your analysis is based on. As someone who takes care of infrastructure, I would rather start addressing IPv4 exhaustion problem with something other than double or tripple NATting, and provide a solution that is already working when others are screaming for lack of foresight.
To the people suggesting we could have taken an alternative approach to IPv6: any changes to IPv4 would break everything anyhow, so you might as well come up with a solution designed for the long term. NATs are tolerable up to a point, but once you double or n-Nat, then you are in a territory where doing things properly would have been better.
Certainly IPv6 probably creates new problems, but not ones that can't be solved with the proper tools. For example, you lose the apparent security of a NAT, but at that point Firewalls are already providing an alternative and capable solution.