Yes, I believe we're at the limit of what we can do with electromagnetic radiation. That's not to say that there aren't other forms of wireless I haven't thought of, but we've been trying to squeeze bandwidth out of the electromagnetic spectrum for over a hundred years now, and its limitations are pretty well understood at this point. If we're all carrying neutrino-based communication devices in 2050, I'll be happily proven wrong.
This is not to say that there isn't exciting stuff going on in the QRP DX world (like JT65), but we're not breaking through the power-bandwidth-distance frontier, just finding interesting new ways to trade the three off against each other.
This is not to say that there isn't exciting stuff going on in the QRP DX world (like JT65), but we're not breaking through the power-bandwidth-distance frontier, just finding interesting new ways to trade the three off against each other.