It's definitely been slow for Python 3 but in my experience most new projects are using it now. The mainstream distributions are planning to make Py3 the default Python in their upcoming releases. Almost all important libraries in Py2 have been ported or replaced by now. There are still some curmudgeons that haven't gotten the memo on Py3, but they'll become almost non-existent over the next year or two.

Python 3 adoption was a little slower than may have been ideal, but I personally think it was a very successful way to implement breaking changes, especially when it could've been a libav/ffmpeg-style mess.