While I don't think the idea makes a lot of sense (Pinkdot anyone?), it is pretty cool.
Serious question: why send these from a warehouse? Why not load a flat bed truck up with 50 or so, and drive it to the closest point that all 50 deliveries share and then release them from the back of the flat bed all at the same time. The video linked in the post shows a drone being launched from a warehouse; not too many people live near amazon warehouses.