It's been known for a while now that you can generally add 2 TFLOPs per year to a console since 2016, PS4 Pro came to market at $399 with 4.2TFLOPs, Xbox One X launched $100 higher with 6TFLOPs a year later in 2017, but this was a console that Microsoft knew they weren't going to sell vast quantities of and wanted to make money on instead.
Launching the next consoles in 2020, should allow for a $399 12 TFLOPs console, and nothing about the Series X looks particularly expensive beyond its specs. The 'Series S' (Lockhart's possible name) would likely cut down on hard drive, graphics, disc drive, cooling and size, which could brind the entry price down quite a bit, it isn't impossible for them to hit $199 and $399, but it likely depends on Sony's price point, as I doubt Microsoft will start the generation at a premium price.