That's if ETH failed to swap PoW algo for PoS algo, 6gb GPUs won't stop been hot cake for miners because they support many other algorithms as well.
Gtx 1060 GPUs are still working. They will continue to earn money for those who want to use it in mining. All this time they have been doing good work for The and other algorithms. They consume a little more energy than newly released GPUs. This is perfectly normal.
It won't be once 23MH earns miners 0.22$ per day, there won't be enough to pay for the electricity bill unless the miners have free solar power or something else, in this area I believe the RX580 8GB is a better option, power consumption wise.