I don't agree that it has. IPv6 is clearly better (no collisions between address space and thus no NAT requirement), and it's perfectly accessible to anyone who actually tries. I'm not by any means a top tier network guy but even to me IPv6 is dead easy to setup. The problem with the v6 transition is that people have very inaccurate views on one or both of those points (usually they falsely believe NAT provides security benefits, or they falsely believe IPv6 is a difficult thing to implement). I'm not sure how to fix this widespread misinformation but that is the problem from what I've seen.