I think it would be nice if desktop users had the option of displaying a lock screen message both on startup and after locking the screen. Many other systems give this option (Android, iOS, etc). In my use-case, I add an email that can be used to contact me in case someone finds my phone. There used to be a GNOME extension that did this but
- it only added the message after locking the screen, not on initial boot, which is arguably the more crucial time,
- it has not been maintained for a long time, and
- this seems like a useful-enough feature that it should be in core GNOME.