Is it possible to create an item teleporter using minecarts+dumpstops?

I notice that when minecarts are stationary on top of a minecart stop that has been constructed as an auto-dump stop, the items deposited within it appear very quickly (possibly instantaneously) at the dump tile.

Is it possible to build a chain of autodump-stops that dump into one another in sequence, with minecarts positioned atop them permanently? The idea being that you cause your dwarves to dump items into minecart 0, and the items get autodumped immediately at some far-off location; this would naturally require significantly more resources than a normal minecart route, but it could potentially be faster.

My guess was that an auto-dump stop would not be dumping to the minecart in the adjacent tile, but rather to the ground underneath it (stopping this idea short)

It will not work in this manner. Your final guess is correct: minecarts do not dump into other minecarts, either on the same level or if they dump down a z-level (or more) (I had tried that second one just a few days ago.). However you are correct about the dumping speed. The item goes from held by the dwarf one tick to dumped in the new space the next (I just watched such an interaction tick by tick). So if there were a way to dump directly into minecarts this exploit could work.