Seems like theft might be an important practical concern for autonomous delivery.
Redwood City is a good test site for this, because it has both good and bad neighborhoods close together. They can find out how much people will bother it.
For historic context see the early adoption woes of traffic and speed cameras.
A siren, cameras, and GPS feedback doesn't help against a molotov cocktail thrown with a mask, from around a corner, or high above; and lots of people don't like the idea of robots roaming the streets.
OTOH, they are probably less of a nuisance than delivery trucks blocking the streets.
http://www.iflscience.com/technology/hitchhiking-robot-manag...
I haven't thought through the economics on these systems, but there are enough startups working on it for me to think it must be a larger market than I realize. I wonder what the overhead is (how many robots you need to meet demand), how quickly they can deliver, and what other limitations they have (temperature control, weather resistance, ability to traverse stairs/elevators).
At what point do these machines become cheaper than humans? I understand that they are likely meant to be a supplement as opposed to a replacement, but until they can compete with humans there's not much of a business.