This was expected eventually because XQD is 4 pipes, streams, which the CFExpress is 4 and 8 pipes in two versions, type A and type B
So older Nikons will likely be updated with firmware for XQD cameras for Type A only but all newer cameras will be compatible with Type B
Sony will not leave the card market, they have announced 1700mb/s CFExpress.
Sony uses the XQD in their pro video cameras...and it is interesting to note none use 2 slots...because it was designed to be extremely reliable and it is. They have reported after millions made, only 1 failed. The differences are vast, not only are the contacts of a design that are protected and superior connections. They are also more like error detection/error correction buses based on the super reliable PCIe+ architecture.
SD cards are essentially a solid state 5.25-inch floppy disk, the with the same dumb bus system without any error detection. The hysteria over the lack of two cards shows the tech is too complex for Youtube photo gurus to understand. I unsubscribe to any channels that promote that nonsense.
The Z cameras are the only bodies on the market that can use the full capability of the 8 pipe CFExpress and expect a future update that allowed ProRes RAW to card capability, unavailable on any camera less than $25,000. It is not an option with current Sony a7/a9 architecture and surely not Canon.
Nikon was ridiculed for its tag line of "Future Proof" cameras when the Z was announced and the Youtube gurus were pretty vocal about how Nikon was leasing a bad camera. A lot of them staked their reputation on those claims but it was a case of lack of insight, understanding, and vision. They made fun of the S lenses for being too expensive for cheap plastic lenses but later the testing revealed each was the sharpest corner to corner wide open than any other lenses. The 50 is the sharpest lens period and the 24-70 embarrasses the expensive 24-70 2.8 G and E versions in corner-to-corner sharpness, contrast, color, and flare resistance. The announced 2.8 version will be a killer.
The May software update is not a bug fix but a feature addition and Nikon has hinted that the policy of adding features will be a core advantage of the future proofing the Z cameras. The hardware is essentially a blank slate of a tough body, and quality sensor and EVF and everything else is a computer that can be configured to anything the manufacturer would like to add or change. Want better AF? Keep improving the software, it is not limited by the hardware like in a mirrored camera, what more control options, no problem, just write a bit of code and add it to the next feature update. This means unlike the Sony which is built as and treated as a disposable camera, the Z cameras are viable for the next decade, it is certainly built to last.
Sony might switch their production facilities to the CFExpress soon but there will still be a good supply since XQD is still the only available pro grade card.
Due to the obvious advantage of pro cards, SD will not be around much longer in any serious cameras. No "pro" camera will have SD in the next releases.