And that's why we now have BOTH /etc/debian_version AND /etc/os-release. Systemd didn't lead to debian getting rid of the former. So now, not only do you have people writing code that behaves differently (or, more likely, breaks) on different OS versions, it has two different files that it will look at for this.

I wonder how long it'll be before the contents of that file start resembling a user-agent string, complete with "Ubuntu-16.10/Compatible"