Imagine a hockey puck sized Roomba that docks at the top of the bowl, off to one side, that slides to the bottom after every flush and then scrubs it's way back up to the dock.
But vacuuming takes time. You have to get the vacuum out of the closet and run it across the entire room. Cleaning the toilet consists of leaning down to pick up the brush, swirling it around to clear off the pieces of poop you just left behind, and putting the brush back. You can do it in less time than it takes to flush the toilet.
The answer is lasers, and a powerful exhaust fan. There probably should be an occupancy sensor to prevent a late night poop ending with an emergency room visit.