Will an M Key motherboard connector always support NVMe, or

Differences Between M2 Cards M2 Slots Keys Sizes and Types nvme m 2 slot motherboard Never used an nvme before So this is new to me If you look at below image, you see the motherboard got two m2 slots One with a heatsink nvme m2 slot 2 drives are “keyed” at one end so as to prevent the end-user from inserting them in an incompatible socket PCIe NVMe drives are 'M' keyed SATA ones,

nvme pcie 40 in 30 slot Why the 4x NVMe? Why not a mix of NVMe + SATA III SSD? Add in cards to go in an empty PCIe slot 1 or 2 drives in one of