68kMLA

Looks like it's just "the existing SSDs" connectorized so unsure how Apple would block this.

Right of First Sale (IIRC) in the US gives consumers the right to modify whatever they buy in whatever way they want and even resell them. Check out the Modbook from the mid-2000s as another example of this. (could dovetail with some other concepts for this specific application.)

Check the SN against it's original config and refuse to activate if it mismatches? Modern apple would do that. I work in the repair industry and am very bitter towards apple because that's just the kind of stuff they pull.

I think even the NAND has to be SN matched. I swear I was watching the video of dosDude working on a Mini where he had to do that before installing them.

It still gives me good vibes of all the upgrades we used to enjoy back in the day (Newertech, Daystar, etc.).

I'd love to upgrade the SSD in my Studio. It would require two components and about an hour of reflashing to do the upgrade from 512GB to 2TB. Will Apple let me do this? No, they'd much rather I buy a whole new Mac. Environmentally conscious, my arse.

Weirdly, there's precedent for upgrades on the Studio because the previous Intel Mac Pro used that same process and very, very similar modules.
Weirdly2, the Apple Silicon Mac Pro, which is AFAIK basically the same computer as the Studio: https://support.apple.com/en-us/101836