I imagine since the IO complex is on the SoC level, you retain most of the magic. The handling of decompression in hardware, the DMAC, the SRAM cache, the offloaded check-ins and so on are all still there with your third party M.2 drive, the drive just has to offer fast consistent performance.
If you're familiar with the Apple world, it's like the T2, which in models with removable flash sticks (iMac Pro, Mac Pro), the T2 remains on the system board, the flash is just dumb fast flash, and that's all Sony really needs from a third party drive, except in this case it'll come with another controller.