There are, have been, and always (?) will be profitable coins to mine. You seem to think everyone with a GPU mines on ETHash. Many people have already jumped off that ship into other algorithms!
They won't be profitable any longer after the enormous gpu mining power jumps from ETH to other coins. That will create a massive explosion in difficulties for all coins. Thats the main point here.
I still feel like we are not on the page here, guys. It's not about the fate of ETH, it's about mining power and difficulty of all altcoins.
But what happens with coins when difficulty rise?
It becomes more worth buying the coins than to mine them - the price of these coins rise.
Higher price of coins makes it a little bit more worth to mine them.
If it still is not worth to mine them people stop mining them and difficulty goes down again.
Decreasing difficulty makes it more profitable to mine them
Everything stabilizes at a higher difficulty and higher price level where it gets profitable to mine again.