A possible problem is that anytime you have a reflection that's not normal to the surface of the reflector, the polarity of the e/m wave can be rectified depending on it's original polarity, whether this is radio reflection off the ionosphere or sunlight off of a puddle.

Another is that to be sensitive to different polarizations, you'd have to reconfigure the antenna either mechanically or electrically in sync with the carrier freq of the transmission. For megahertz, i'd say mechanical is out of the question, but I'm just ignorant enough to think that it could be possible.

What did you have in mind specifically?

and...

What benefits would it offer over existing systems. I mean, we could communicate with Europe using a row of ships across the atlantic equiped with semaphores but I think the internet works much nicer.