Stated Goals
Googles original vision for this project was to deliver defibrillators in an emergency to inaccessible areas and its stated enlarged goal is for delivering emergency items in areas where the infrastructure has been decimated, through earthquakes or other natural disasters and war etc. Also the possibility for the delivery of drugs or medical devices to people in inaccessible areas holds great promise...
It is not being developed as a home delivery system although should the tech become good enough in the future that may be possible in certain suitable areas..
Collision detection is routine on most high end drones now along with image recognition, real time 3D mapping etc etc and getting better all the time. As it currently stands it's in its infancy but it's aims are achievable with current technology.