They are only profitable because eth is profitable, that is called the chain effect, that is why cryptocoins are valuable, because bitcoin is valuable. If no more eth then what is the enxt coin profitable as much as eth? there are none, so nothing will carry that much hashrate or even the demand for such coin, meaning of this thread is gameover for now is getting very close, yeah could be another coin in few years but that will take time, I believe it will have another coin as good as eth to mine.