Uilleam :
What I see happening is when the new 2060, 2018's come out in a few months it's going to cause a flood of older cards to hit the used parts market. Miners will snatch up the newer cards and there will be plenty left on the shelf because your average gamer will just buy an older card for less which will mean there will be more supply than demand. Sales will spike briefly for video card makers then come to a sudden halt.
If the old cards are still able to turn a profit, why would they get rid of them? They'll just continue to use the old cards, in addition to buying up the new cards. The only thing likely to make card prices drop quickly would be if governments started putting heavy-handed regulations on cryptocurrency, scaring away investors. Or perhaps if specialized mining hardware appears that makes mining on video cards obsolete, as happened with Bitcoin some years back. These newer currencies are designed to be resistant against that though.
Otherwise, it seems likely that prices will only slowly decrease over time, as they did after the more limited price spike last summer. Even after half a year, prices weren't entirely back to normal though, and then this most recent spike occurred.