It is not a remote theoretical possibility but just that no one has attempted it, the PID 1 such as systemd can be replaced with an infected version of systemd and then imagine what's not possible once you as malware yourself are systemd, the ring master.
This Linux superiority complex isn't rooted in reality, not that I'll ever pick Windows as my daily driver.
I like and been using Linux as my personal and work computer for decades. But I don't delude myself about what safety is inherent to the system and what just about popularity.
This Linux superiority complex isn't rooted in reality, not that I'll ever pick Windows as my daily driver.