To me the most straightforward thing to think about is EM waves at frequencies we can only imagine. Very different sources and detectors from what we have, therefore the radiation is undetectable to us (also very line-of-sight), but still the same physics in terms of the properties-of-the-universe required. I would imagine this increase would be developed for the same reason we have gone from KHz to GHz in a hundred-odd years: The higher the frequency the more information you can transmit per second.