Industry sources claim that Microsoft has chosen Phison as the SSD controller supplier for the upcoming Xbox Series X, so there is a fair chance we could see PCIe 4.0 read speeds of up to 7,000 MB/s and 1 million IOPS, essentially allowing for more detailed textures, smoother gameplay and lightning fast load times.
https://www.notebookcheck.net/Upcoming-Xbox-Series-X-consoles-could-benefit-from-PCIe-4-0-SSDs-thanks-to-Phison.450199.0.html