One has to wonder if it would still be more expensive to use one single stack of this vs all the top end vram chip(16)/associated power delivery/circuitry/cooling/PCB(thicker and/or longer).
If it's still more expensive that's quite impressively bad and a miracle AMD did HBM at all years ago.
At least for ultra high end cards(5090) one would think it would definitely be a doable thing. Lower total wattage consumption and more than likely keep it cooler.