Also Gentoo since mid-2018.

Although their package management requires manually specifying the minimum accepted Python version for every single package, so they have thousands of packages that would run just fine on Python 3.7 but no one has the time to manually check and label them as such. So their default is still 3.6 and using 3.7 as your default version is not well supported.

I wish someone told me Gentoo is a non-starter before I wasted an afternoon installing it.

While we're on the topic, it's pretty stupid how PEP 394, the one that says "python should point to python2.7", gives its reasoning as "because all Linux distros except Arch do it this way" and then all the distros say "python should be python2 because the PEP says so" for the next 9 (maybe more) years. How is anything ever supposed to change?

My mint 19.2 installation does the same. To run a python 2 script I have to run my conda python 2.7 install now.

Is Manjaro included in that?

Edit: Yes Manjaro has default Python3 too. :)