I don't know anything about RAMs or their bus size. Is this something that will be "fixed" in the future, idk, with DDR6? Meaning we can have replacable RAM with such bus.
So to ensure 256 bits @ 8000 MHz works well AMD did it in the same package. In theory they could A) ship a halo without ram B) design a new socket, C) allow motherboard makers to pick 2 x CUDIMMs or 4x DDR5 dimms. Not sure that would buy them much market though.
As apple and others have proved, not many care about replaceable dimms, especially if it gives them 2-3x the performance and/or better perf/watt.
This is also being seen in the X3D CPU's where the memory is stacked on top to reduce latency and as density was maxed in 2d space.
It’s also not that absurd pricing of the modules themselves but of the R&D effort to cram 4 CAMMs onto a board with sufficient signal integrity