Fortunately no one ever built a prototype:
http://blog.modernmechanix.com/compressed-air-to-shoot-packages-into-moving-train/
A bet the inspiration for this invention came out of a bottle. 
Cool!
A more modern take that Amazon could get behind would be to use drones to add and remove packages from moving trains. Special racks could be added to the tops of low-cube box cars to accommodate mini containers. Big bar codes on the top of the container would allow the drone to identify and remove it’s assigned container.
Not any crazier than the air torpedo, is it?
Sounds like something Lionel would come up with.
I got some packages delivered to me that look like they were shot out of a cannon!!!
-Kevin.