As far as I am concerned, a mere user, hacking python for 'academic research' in multiple aspects of structural biology and bioinformatics, I have yet to see a single practical argument for switching to or even investing time in learning Python 3 'right now'. Maybe in six years it'll be a different story, but from where I stand, python vs python 3 is a remote and ephemeral distinction, created by the grand poobahs, of zero to little significance for me.
Scientific code typically translates cleanly using 2to3, even. You can get up to speed with all those "terribly complex" changes in Python 3 in about five minutes. Scientific code in particular typically has no advanced unicode handling and no custom CPython extensions, so switching is trivial.
I totally agree with you: Py 2 vs 3 is of very little significance to us scientists. Which is why I use Py3. There's nothing to gain by sticking with Python 2, and almost no effort at all to go Python 3.
As an example of why Python 2 is going to be the primary Python for me due to circumstances beyond my control, the following two are examples of open-source "Python" software I (and a huge percentage of the structural biologist community) use for 75%-85% of work:
Both work on Python 2 only! So guess what, I have to write all the extensions and analysis plugins in Python 2 if want them working with those packages.
Want to even dare trying to move those two packages to Python 3? See you in a decade!
Why should I even bother with Python 3?