I've seen multiple Youtubers post mining videos about CPU mining and Threadripper in the past few days. We might see shortages of the 1950X and increased pricing/shortages of older, higher L3 cache Xeons and respective motherboards, especially if CryptoNight-based currencies return to higher profitability. There are other CPU-friendly algorithms, too. I built a Threadripper 1950X system a few weeks ago partly to mine with (more for Nimiq than CryptoNight, though I am doing XMR at the moment), but total system cost doesn't make it worth it to build new Ryzen/Threadripper PCs just for mining unless you are okay with longer ROI than is typical with GPUs or ASICs.
Used servers (mostly 10+ core, dual socket Xeon) are a slightly different story, depending on price.