The reason that Destiny would not work on the WiiU is simply because the WiiU lacks something important that all the other major systems have: A reliable online gaming system. While the WiiU is pretty close to the current gen systems, hardware-wise, it doesn't have a setup anywhere close to Xbox LIVE or PSN. Add to that the very small user-base of the WiiU due to Nintendo's terrible job marketing the console, and there really is no good reason to even attempt porting a game like Destiny over to it.