Distros that use Python 3 by default (such as Arch and Gentoo) still allow for Python 2 to work side-by-side with Python 3. Proper separation using virtualenvs works seamlessly, and there's no problem at all to work simultaneously on Py2 and Py3 projects.
Then after reading your comment, I remembered that my complete switchover was triggered by the default version switch in my primary machine's distro (Arch).
So indeed, these things do matter for real-world adoption of Python 3.
From the two sections in here it appears that Fedora will stick with `python` pointing to Py2, so that's good news.
Arch switched to python3 as the default "/usr/bin/python" with no way to change it because of their persistence on following the upstream. They payed the price by having to hunt down and modify all the python2 scripts.