Before we get ahead of ourselves, it's worth pointing out that the Mac Studio (M2 Ultra) has a similar storage setup, but custom upgrades are difficult to do: the computer uses Apple's own bespoke SSDs, you can't just slot in any off-the-shelf replacement.

However, as noted by MacRumors, it’s probably similar to their storage with only the NAND chips on board and the controller is still embedded in the SoC, tightly restricting any possible DIY upgrade or repair options.