There are a handful of other PoW coins not far behind Ethereum so I wouldn't count on demand plummeting
In my view, this site is strong evidence for the thesis that demand for GPUs will plummet, here's why:
1) If we tweak your link to sort by Market Cap, we can see the next biggest coin to mine after ETH is has only 1% of ETH's market cap https://shorturl.at/lxLS5
2) These smaller coins do not have the capability to automatically or naturally grow bigger market caps, trading volumes, and buy-side demand just because ETH switches to PoS. Mining profitability ultimately comes from a coin's buy-side demand, which is proportional to many things-- fame, developer activity, etc.-- and none of the PoW chains in that list are anywhere remotely close to "breaking out" and growing proportionally with Ethereum, or, say, Solana. How do I know this? Well, I'm an insider that focuses all of his time on ethereum and web3, you'll have to take my word for it :)
> These smaller coins do not have the capability to automatically or naturally grow bigger market caps, trading volumes, and buy-side demand just because ETH switches to PoS.
What would they need to cross that barrier? For example, don't all coins have the ability to manipulate trade volume by sending money between owned wallets?
Why sell a GPU for a fraction of the price, when you can just switch over to another coin and make 50-90% of the money you were making still.