This is untrue about Arch, but true about Gentoo and seemingly will be about Fedora. Your experience with "Py3 default distros" has a bit to do with what version `python` points to. You certainly can get by with virtualenv all over and / or setuptools rewriting shebang lines but it's less convenient.
From the two sections in here it appears that Fedora will stick with `python` pointing to Py2, so that's good news.
What Fedora is planning is leaving /usr/bin/python pointing to Py2, but making all their tools explicitly depend on and request Py3. This is distinctly different from the Arch decision, which instead resulted in fixing everything that expects `python` to mean Py2 to explicitly request Py2, or assisting with the porting process to Py3 for those applications.
From the two sections in here it appears that Fedora will stick with `python` pointing to Py2, so that's good news.