https://social.heldscal.la/url/635960

> Based on the rate of uptake for Python 3 libraries and the rate of decline for Python 2-only libraries, the Microsoft team predicted that 3 will overtake 2 by "around May of this year."

That's in number of uploaded package versions each month. Interestingly, py2+3 packages are the largest category of packages, beating both pure py2 (since May 2014) and pure py3 (since forever), and py2+3 is still growing faster than py3 too.