Inspired by this video on rabbit breeding and @Carpdime’s diagrams. I was looking up random things on Youtube and saw the video. Breeding rabbits. IN WINTER. So, obviously I had to watch that. And it made sense. Then I wondered, “what about fluffies?”
As @AMDk7 opined in the comments (before I could write this up), it does indeed resemble a cat litter box because why reinvent the wheel? In fact, my cat’s litterbox is very much like this except for the drainage grating and removable tray/pee-pad not being there. Fluffies are closer to cat or dog size than rabbit, I think, so the inspiring nesting box didn’t quite seem right.
I liked the idea because it made a certain amount of sense to me. Since fluffies are generally on the small side, I could see this fitting mama and babies comfortably (easily) or the whole family (mama, papa, babbies) rather snugly. A feature to be sure (fluff-pile, warmth, etc). Adding the nesting material (assumedly from any pet shop or farm supply) would be cozy and fulfill nesting instincts if present in your headcanon. I’d imagine fluffy fluff would be easily obtained (how nicely or unfairly is up to you).
Having a limited in and out would be somewhat reassuring, similar to the classic alleyway box. Can see out of it so its not a sorry box, but still feels protected. An adult might need to stoop to get in, but I don’t see that as a problem. Again, more cozy and secure feeling. More private and safe.
Not a replacement for a litterbox. The grating is there for adult accidents and babies who have no bowel control yet.
I see this for home/pet fluffies, some shelters/rescue operations with pregnant dams and perhaps a bit more funding, rescues/refuges, and low-volume breeders (not sure how this compares to Carter’s Creature Comforts by @BFM101). This would be one part of a larger enclosure.