That would depend on how they designed the memory controllers. GDDR6 only supporting 1-2gb modules at present (I believe GDDR6W supports 4gb modules). If they were using 12 1gb modules, then increasing to 24gb shouldn't be a very large change.
Honestly, Apple seems to be on the right track here. DDR5 is slower than GDDR6, but you can scale the amount of RAM far higher simply by swapping out the density.
Honestly, Apple seems to be on the right track here. DDR5 is slower than GDDR6, but you can scale the amount of RAM far higher simply by swapping out the density.