Even in markets where cars are used a lot for food delivery; I can't see it really working very well. It's hard enough trying to schedule food delivery drivers being in the right place at the right time (often waiting a while for food to be ready if the order got delayed in the kitchen). Trying to then piece together humans going places in between seems virtually impossible.

However, if you allow yourself to simplify the problem, it seems there is really no physical difference from a food delivery and a ride. Pick up at one location, drop off at another--maybe with extra time required to get out of the car. In both cases, there is a limited allowable waiting threshold.

So if you can merge those work forces, you could attain higher utilization. The main problem I see though is that both sectors surge at roughly the same times, so it isn't quite as complimentary as you might initially hope.