I don't think AI will create a coin superior to Bitcoin. However, various tasks can be performed with AI. For example it can develop a more successful bot for trading. When trading, bots usually trigger each other, that leading to sharper ups and downs. Since the amount of circulating coins used for trading is decreasing daily, this could pose a minor threat. We may see more volatile price movements. Other than that, I don't think AI will pose a serious threat to Bitcoin.