Apart from the technical difficulties of dealing with controlled super high frequencies, and the danger of seeing inside my head (it's a dark, dark place!) you should consider why we use X-ray and gamma rays in existing applications. X-rays are used because they are easily blocked by dense objects, thats how they produce photographs to show our insides. Gamma rays are used to sterilize food stuffs because it destroys organic nucleii. Both are very good reasons not to use them. One would have a very short range, the other might kill you. When you quite correctly state that data rate is proportional to bandwidth and that is limited by frequency, you are missing the point that the Nyquist limit is basically two carrier cycles per sample so even at much lower frequencies the theoretical data speed is faster than we ever need.
Brian.