I think the problem is that python 3 is just different, without much improvements over 2 for many people. For example, the things which IMO were worth fixing at backward incompatibility price (like the import system, improved C API with ABI across minor versions, packaging) were not fixed.
I have (in small parts) contributed to the python 3 conversion for numpy/scipy, and the only reason why I have done so is to be a good "python citizen", and because numpy is a major library in the python ecosystem. But I don't see any advantage in doing so. The cost is high, and the advantages near inexistent for me
You see - the reason your hit list of itches were not fixed were because no one stepped in to do them - this isn't anyones fault, but it doesn't mean important things were not fixed. Instead, the other itches (such as bytes vs. strings/unicode) were fixed.
Function annotations, the standard library cleanup, and other things came along for the really big ride, which was the bytes/unicode/etc ride. So, there's lots of improvements that came with 3.0 - but the nice thing is is that it continues to evolve.
We now have a New (more rational) GIL, we're probably going to have a futures package (http://www.python.org/dev/peps/pep-3148/) and so on (heck, python3 is also getting a jit). And things will continue to be added. Everyone knows and admits that the transition will take years, but now with 2.x being "done" (meaning, no more releases past 2.7) and more great work being done in 3.x, hopefully people in general will start to see the benefits.
I have (in small parts) contributed to the python 3 conversion for numpy/scipy, and the only reason why I have done so is to be a good "python citizen", and because numpy is a major library in the python ecosystem. But I don't see any advantage in doing so. The cost is high, and the advantages near inexistent for me