Note that python3 still doesn't have widespread adoption, because there are still widely used libraries lacking support for it.
But we are missing the point here. PHP could need a cleanup from the ground up even if they have to break a lot of stuff this could help the language to evolve.
Don't bet on it. It has been too many a years already, and no dice (or minimal dice)
Having listened to several Python core developers as well as core developers of some major web frameworks and libraries, I have no doubt that Python 3 will replace Python 2.
I think the key tipping point will be when the major web frameworks support it.
The official party line on the delay was the lack of a WSGI spec for P3, but there has already been one for several months now.