[rbanffy]

Many people use Python 2 for the sole reason it's the default system Python. I assume a lot of them will instantaneously move to Python 3 the moment typing "python" on the command line will invoke the Python 3 REPL.

All my python 2 only code explicitly invokes python 2 on the shebang line.

[collinmanderson]

Though, more likely they'll find that typing "python" returns "command not found", and in that case they might find it easier to just type apt-get/dnf install python.