Interesting. If you look at bagage moving around in the basement of an airport, I can imagine how someone's imagination could see containers moving on their own or in small groups over rails.
On of my first objections would be air resistance. As a freight train driver, I really noticed the difference between a fully loaded container train or one with empty spots.
On the other hand, the average speed of a freigt train (from container entering the yard by truck until leaving a yard by truck) is pretty low; would you put that container on a rail chasis, it could leave instantaneously on the 'conveyer-rail-belt'. So even when the maximum speed could/would be low (avoiding air resistance), the time between departure and arrival could be better then conventional.
Ow, I'm not sure how Amtrak fits into this. The distances are to big for this principle: YouTube
It's fun ...
No more people complaining about long trains blocking streets. Instead, more people complaining about railroad crossings being constantly active.
Tingtingting ... railcar passing ... wait for it ... tingtingting ... railcar passing ... until something somewhere breaks down.
So you need to get rid of all railroad crossings.
And you need double track or directional running everywhere.
Railcar controlled powerswitches everywhere.
Well, interesting food for thoughts, but still, for the near future, nah...