> Surelly with a bit of backward compatibility sacrificed like 2 vs 3.

After 10 years, the 2to3 transition is still ongoing, and lots of companies will be dealing with python2 code for a long, long time. Breaking backward compatibility was a terrible decision. Breaking it again now that most libraries and open source projects have finally moved to python3 would be suicide.

Programming languages should take backward compatibility as one of their most important features, because of the hundreds of millions of lines of code already written and that would need to be changed and validated. This is especially true in a dynamic language where you can't even rely on the compiler to point out the issues.