Comment 7 for bug 1283871

". It just so happens it's only one of the few "well-known directories" that Shotwell defines."

I'm surprised at this assumption. DCIM (and filename rules) are part of now-ancient standards for digital cameras:

https://en.wikipedia.org/wiki/Design_rule_for_Camera_File_system

Mobile phones with cameras have by long convention also offered this filesystem layout. My current iOS 9 device still does this, for example.

This is nothing to do with Shotwell's preferences.