GPU mining is stupid. All this electricity and heat generated so a few of us can profit from a digital currency that does not exist. It's really ridiculous when you think about it. But a lot of the world is ridiculous. Central banks print money and 75% of the world lives in poverty. So as stupid as GPU mining is, it's just building on the stupidity that already exists.
With that said, the future of GPU is not going away but it should transform. GPU companies are going to cash in and they should but they can develop products that are more efficient at what they do on the consumer level. I think what the OP wants to know, is what is the future of GPU mining when Ethereum goes POS:
1. People will switch to mining another coin, since it won't be nowhere near as profitable, it won't last long and we'll get a big GPU sell off
2. The big sell off will eventually be a positive to those who hung in there. How much of a positive? Impossible to know.
3. As time passes, another (profitable) GPU mineable coin will emerge that needs people to mine and build the network.
GPU mining is building an infrastructure. Right now the majority of that infrastructure is supporting Ethereum. This will switch to something else. Crypto was just born, it's hard to know what will happen tomorrow, let alone next month.
"just building on the stupidity that already exists"
LOL
Could be a slogan for a company or politician...maybe President Camacho
I have to commend you on the President Camacho reference -- two thumbs up!
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I have gotten heavy into GPU mining (around $60k in hardware)... but I do very little Etherium (Dagger). I sold 75% of my AMD cards on e-bay for 50-100% premiums after using them for 30-60 days and bought a bunch of GTX-1060s & 1080s.
I feel like they have enough time left in them mining *something* to pay themselves off and then some. I'm already to 50% of my hardware paid off so, frankly, I'm not sweating much.
As far as the OP... yes when Etherium mining ends it will hit other Alts pretty hard... but I get the feeling we still have a fair amount of time and if you mine / hold a bit with coin appreciation you will come out good (that's my bet anyway).
PS: With the cost premium of the 1080Ti I've been sticking to 1060s... I have a single 1080Ti and it doesn't really blow me away by any means for the cost. I can get almost four 1060s for the same price.