Well they did mention one specific, and that is the fact that this service is only for DashMart orders i.e. the first part of any autonomous delivery order is at a DoorDash -controlled and -staffed facility. Where they can babysit the process.
To me that pickup part seems almost more difficult than the delivery end of the journey. If you think about a busy restaurant with app-delivery orders piling up on the counter, how is that order going to get into the autonomous vehicle outside or down the road? Maybe a new service will spring up called mini-Dash where a human has a job running the orders down to the waiting vehicles?