Sounds like a perfect application for Micron/Intel's (yet to be widely commercialized) 3D XPoint[1] :) Although I find it highly unlikely a new Xbox would be the place to debut the technology.
Regardless, claimed latency is between DRAM and NAND, so I wonder if it would be performant enough for a gaming use case. To mikeash's point, 3D XPoint is byte-addressable, so perhaps it's possible...
3D Xpoint has been commercially available for years under the Optane brand name. It's much more expensive than NAND (16 and 32GB NVMe drives available for ~$2/GB) but a smallish amount in the Xbox acting as some sort of cache seems at least semi-plausible and would fit with the "next generation SSD" and "virtual RAM" statements.
Regardless, claimed latency is between DRAM and NAND, so I wonder if it would be performant enough for a gaming use case. To mikeash's point, 3D XPoint is byte-addressable, so perhaps it's possible...
[1] https://www.micron.com/products/advanced-solutions/3d-xpoint...