The internal SSDs in the new Xboxes are only 2.4 GB/s, which doesn't even max out the bandwidth of PCIe 3.0. Most mid range NVMe SSDs these days are at least that fast if not faster.
They're also only using 2 lanes as is the expansion slot, so you're going to need something with twice the speed to match the internal drive.
Did everybody miss the part in the article where they're using an almost identical model m2 drive to the one that's already in the Series X?
From what I understand they actually pulled it from an xbox so we really shouldn't jump to conclusions yet.