I’ve had exactly the same idea! Living in LA I sometime imagine how the city will look like in hopefully ten years or less when robots pick up all the litter! Hopefully there will also be landscaping robots and sidewalk/road repair bots too.. those three pretty much are what you need to turn any rundown neighborhood into a sparkling oasis it seems. My other near term idea is just robotic city trash cans, that slowly crawl down the sidewalks on a loop and empty themselves into a big bin in the alley or whatever as part of that loop. I think people probably wouldn’t mess too much with the litter bots either, especially if they work a lot on the sides of freeways. Also people don’t seem to mess too much with the cocos out there delivering food three blocks..