whattomine is just a snapshot of most profitable coin to mine on particular day. It doesn't means its practical to mine for a long term. I agree with @cryptogenius. And Metropolis update is near, it's meant to make the difficulty so high that it's not mineable anymore aka Ethereum Ice Age. Refer to my post! https://steemit.com/ethereum/@tngflx/metropolis-ethereum-hard-fork-what-you-need-to-know.