Hoping a more futuristic route instead of GPU. Perhaps a smartphone chip maker can come up with mining on their specific chip thus making it special and valuable. Of course then the algorithm may need some changes to suit it. But it will become viable since people need smartphones. Today almost all are very similar if you have a snapdragon highest chip. For example Xiaomi or Huawei just smaller chip maker but they could make it happen to their advantage. So users of their chip will be able to mine while other chips unable or maybe able if they cooperate . Then we have a truly distributed network since smartphones are everywhere, faraway places and more.