It all depends on when Eth 2.0 moves over to PoS. Ethereum currently has over 800 TH/s and other PoW coins such as raven and ergo only have 7.48 and 20.34 TH/s. When Eth moves over, all that hashpower has to go somewhere, so likely people will jump to the next profitable coin, except those coins are only profitable because difficulty is low. When all that hashrate moves over, difficulty will drastically spike and profits from mining will plummet. It all comes down to how well these alternative PoW coins can handle the hashrate. Eitherway there's going to be a steep dive in profits from GPU mining and those who got into the game late will be lucky to reach RoI. It's hopefully at this point that people start panic selling their GPU's on the used market. Fingers crossed Eth 2.0 doesn't continue to get pushed back and occurs sooner rather than later.