Not even sure where you would find 4 or 8TB m.2’s in a 2230 configuration. I don’t know if their 8TB offering is a single 8TB device or 2 4’s in raid 0.The SSD there though appear to be DRAM-less and controller-less. So it's unknown right now if you can do a user upgrade.
But they are probably Apple custom chips, but they are easily accessed so that at least leaves the possibility that they can be later upgraded or replaced.