I'm certainly not long on uBeam (even after this fragile demo), but what physics dictates that it won't work? Sure, you're certainly going to take an efficiency loss, but wall outlets already output far, far more power than your phone uses while charging, so the real questions are how inefficient is it, how safe is it, and how convenient is it (can a final product survive if it needs line of sight?). While these are certainly very difficult and perhaps intractable engineering problems, I'm not aware of a fundamental physical limit on any of these that would limit an application like phone charging.