Ram hybrid drives came to PC about 4 years ago & PCIe 4.0 is already being phased out PCIe 5.0 is replacing it instead! Neither of these will make much difference to gameplay either & pricing aside Sony could just include an SSD right now to make a massive difference to gamers with seamless streaming ingame but as always its about costs & profit margins.PCIe 4.0 and flash / ram hybrid drive (rumoured). Can you get that on the pc yet?
If anyone thinks PS5 will not be an expensive console they are going to be in for a massive shock as all hardware & electrical goods are set for massive price hikes due to Brexit & supply & demand factors in the coming years as consoles & home entertainment dominate modern life for many people at home.
https://www.techspot.com/news/78355-pcie-50-ready-before-pcie-40-can-launch.html
https://www.tomshardware.com/news/pcie-4.0-5.0-pci-sig-specification,38460.html