Except Fortran is, and is going to be, further developed. (So, if a new useful programming concept appears, or a major design mistake is discovered, it always can be patched.)
Python 2 is going to be abandoned in 2020. Python 3 will supersede it.
But Python 2 is Free Software, so as long as people like it, they can keep improving it:
Elsewhere in the thread xrange has mentioned Tauthon. And there are more Python 2 interpreters than just the main C Python.
Pypy may stop supporting 2 syntax officially, but I doubt it. Since it never changes, there's next to no overhead to keeping it available.
And further, if your language isn't changing then maintenance and debugging become much easier. Conceivably the codebase(s) can asymptotically approach 100% correctness.
O_o
So I don't think there's much to be gained.
The 3 syntax and new features are not massively better than the sweet spot hit by 2, they're not even incrementally better. They're just massively more complicated.
So the cost/benefit ratio of Python 2 to 3 just isn't there. People are changing up because it's "the done thing" not because they really gain anything.
I was surprised as hell when I realized I wouldn't use Python 3, but it is a rational and considered opinion.