> That wasn't done, but for reasons that amount to "we don't want to"...
Well, and giant glaring differences in internals. Python3 and python2 have incompatible bytecodes. Swapping compilers on a per-file basis in a language as dynamic as python isn't possible. Python allows dynamic re-writing of modules and source code. How do you decide which version a module is run with if the module is modified at runtime?
That wasn't done, but for reasons that amount to "we don't want to"...
I simply believe the python authors made the wrong choice.