i5-8400 sold very well. Not everybody needs SMT (especially since HT and SMT makes your PC more vulnerable) and this 3500 priced effectively could be the new bang for buck CPU for gamers and general consumers.
It is unlikely Microcenter will be selling cheap CPUs online. Even when you buy CPUs in stores, they typically have a 1 per customer limit. More importantly, Microcenter prices their CPUs much cheaper than competitors at nearly what they cost to procure them as a way to attract customers to the store. I remember working at Microcenter and our employee discounts could never make CPUs any cheaper even though we could get like 80%+ discounts on things such as cables and adapters. It would make no sense for them to offer super cheap CPUs online as it would contradict their goal of marketing their other stuff in their stores.
The Ryzen 3000 doesn't need an X570 motherboard to run. X570 is for people who want fancy new features like PCIe 4.0. I'm running a Ryzen 3600 on a cheap B450M motherboard myself. The Ryzen 3000 cpus can actually run on cheap B350 board from the Ryzen gen 1 days too.
Techspot has a review of a cheap B350 board running a 12 core 3900X, and the B350 can come close to 97-98% of the performance of a X570 board
Surely you've read our 3rd-gen Ryzen review by now. While testing the new CPUs we posed the question, how well will these processors work on a really...
www.techspot.com
So you really need like 50 bucks for a B350 or B450 board to run any of these cpus.