No surprises here. Just like the lockdown on iPhone screen and part replacements, Macbooks suffer from the same Apple’s anti-repair and anti-consumer bullshit. Battery glued, ssd soldered in and can’t even swap parts with other official parts. 6000$ laptop and you don’t even own it.
The RAM is built onto the substrate. Every contact you add increases signal degredation. Plus actually trying to fit eight sockets on a SoC package would be a complete nightmare.
Dividing RAM like that into two pools would violate the permise of the whole unified memory system. You’re really asking for the wrong thing here. Why not convinve them to do something like a modular SSD that’s far more achievable? Also memory that doesn’t come at sky high prices with an actual sensible mimimum (8GB on MacBooks in 2023, really?).
For other laptops there is actually a solution to this problem called a CAMM. It would even work for the M2 Macbooks possibly (not the M2 Pro or Max) if apple are willing to sacrifice size or battery life of the laptop. The reason this wouldn’t work for the M2 Pro and Max is you would need two or four of these things. It would be diffcult enough to fit just one in a Macbook that have tiny, tiny logic boards to begin with.