Two problems with this. There is a very long tail of libraries on 2.x only that are not moving to 3. Second problem is that many 3.x only libraries are not widely used or tested and you'll find obvious errors that would not be there if they were widely used.
And as you said, some popular libs are 2/3 compatible.
So what should an end user do? Build on 3, which still has many things missing and less reliable 3.x libraries? Or stick with 2 which has everything the 3-only ecosystem has and much more.
3.x in reality makes no sense unless you have a political bone to pick. The big attraction was the unicode by default.
Python has supported unicode since 2.6. Python3 presents a new default way of handling it, nothing more. Py3 is pure technical churn at its worst. There's no innovation there. As a result the users outside of a vocal minority aren't coming.