Judging by TX's use of them, I think they're more like ISO files. Basically like images of the carts, that the CFW will trick the device into thinking its an actual cart inserted inside. Then you'll press button combinations to switch between different cart images so that you can choose what you want to play. Like Sky3DS+.
Yeah that could be for the XCI (TX said they are using those) and thats why i wanted to know ablut NSP too. Would they be like cias? Just install and play? No CFW needed after? No way to tell if they are not legal because there are no private headers?