I would be concerned about putting so much weight in the wheel. I know that with car designs, the better/faster cars spend oodles of $$$ to make the wheels as light as possible, using a variety of exotic alloys. Adding a battery to the wheel area itself seems to be somewhat counterproductive. What was mentioned earlier, however, makes some sense and that is to find a way to more evenly distribute the weight over the whole bicycle instead of putting it all on the back. If you want to find ways to conceal the batteries or not detract from the appearance for any other reason you can buy some ebikes that store the batteries inside the frame.