Till ETH goes PoS we can still gain some money. Hope ETH will not go PoS till at least it reaches 800$. Why? Because i think when PoS is applied, small hodlers, (with 5 or less ETH), will not be able to enter the PoS verification system, and they will be forced to sell their coins. A huge amount of coins will flood the market, time when sharks will stay calm waiting for those coins to lowe their prices for them to buy. Moreover, i don't think ETH can survive with only the money from smartcontracts. It has a value of 468$ right now, because it can be traded, bought and sold. Once PoS is applied, my guess is it will go down by a lot.
Once thing is clear for me. Once ETH goes PoS , there will be no more coins profitable to mine in the hole market and GPU mining will die. ASIC miners will last a big longer. There is NO PLACE TO PUSH SUCH A HUGE HASHRATE OF ETH. No way.
I believe the minimum POS staking amount for ETH is not 5 ETH, but rather 32 ETH. That is actually a huge barrier to entry but that does not necessarily mean that people with less than that will sell their coins. There will still be people who will hold their ETH, as usual.
I am however in agreement to your statement that when ETH goes POS, GPU mining will surely come to an end because of the difficulty rise on all other coins. It might actually be better to sell GPUs today while they still can still mine. When profitability goes to 0 the market will flood GPUs even more so.