I think the frustration with tips is so prevalent that the advertising could just be "Skip the tip, simply walk to the street to pick up your order!"

Would work great in suburbs where a robot car could pull in front of home for a minute or two, your food will be bid to another customer if you don't pick it up in 5 minutes. maybe the little robots in NYC are better.

I would argue that the sidewalk robots are too hard to coordinate and not strong enough to hold up against crime, the solution is somewhat closer to my other comment below, a vehicle with maybe 4 or 8 food cells that can fill up at various locations then make its journey around the city. At that point the problem would be idle timeouts and how to handle disgruntled consumers that lost their window for pickup