I'm sure it's not just a stunt but I wouldn't expect this to take off. Not everything Amazon touches turns to gold and so far they've done quite poorly with hardware.
I'm sure they would to have drones simply to have 24 hour delivery and eventually it could mean sacking warehouse staff. The drone can find the item in the warehouse and then take it off to its location. But I think they also realise this is a long way away. It just happens their shareholders let them piss away money.