While we are on the "things that are currently impossible but would be totally sweet" topic, imagine uploading your consciousness to a computer. Coupled with a 3d printer that can print at a molecular level, you have immortality. The problem from there is that once you have that, you can print/program yourself all the dopamine you want, the underpinning of human desire and all human accomplishment. If that weren't problematic enough, all concept of possession and currency will also be lost. If you assume fusion is involved, then it's not a far stretch to assume the manufacture of heavy elements, and therefore, the truest alchemical ideal: sand into gold, platinum, plutonium, you name it.