Oh come on you are really reaching now. The below two points are especially ridiculous.

>
> 1. What if they update the system like this:
>    Backed up user data/script -> Fresh install -> Restore user data/script
>    For that, it won't work.
>

This is called a fresh install and not an upgrade. In this scenario there would be a substantial amount of work anyway... A sane backup in this workflow should include an rpm list to restore anyway (which would then include rsyslog). Would you just do the install and then have over the machine? No you'd do various customisation bits and as an informed admin you know of the change and can add rsyslog if you want.

If an inattentive admin in this scenario you'd do your install and check for problems in /var/log/messages and see the README ... If such a bad admin even that is missed then the person is in the wrong job.

> 2. Like other already point out, Windows/Fedora dual boot.
>    You can see /var/log/messages from Windows, but how can you get journalctl output in Windows?
>

Oh how do you get your logs to read in windows from your lvm/ext4/btrfs filesystems currently in a disk boot scenario?