At this stock price Amazon can do a buy out of FDX with stock and really add actual earnings to their business model. FDX market cap is only about 13% of Amazon's. Offer $150 per share in a stock swap and they are now the 700 lbs gorilla.
If they really want to get crazy, throw in a major cargo shipping company like Maersk and they are now an unstoppable force. No sense having an huge stock valuation if you don't use it for growth.
If they need an end game, then focus on a takeover of USPS after FDX. With their thousands of delivery trucks driving everywhere, making the courier a two person job and in addition to delivering letters, you auto launch drones off the top of the truck to deliver to homes along the route. Then the drones home-in back to the truck to be loaded again for launch as they pass another parcel location. One loader keeps the automated drones loaded and the other one puts mail in the boxes. 6-8 drones per delivery vehicle.
See that's some fantasy land class II string theory type thinking.