Somewhere online I saw mention of a dark AU Zootopia webcomic, so with my love of dark things, I checked it out. While the art is a tad challenging at times, I love the story dearly.
Check it out here.
I had thought the author/artist came up with the "tame collar" idea (all predators have to wear them, it shocks them if they let their emotions get too high). Supposedly it keeps them from going feral/attacking prey animals.
But that was actually originally how the movie was going to be! Check out this deleted scene (animation not complete in it), it's heartbreaking:
Click to view