>The price increase will be very small if manufacturers are no longer able to segment the market to make a higher margin on those who need it.
AMD doesn't have this segmentation. Where's the hoard of people building systems with ECC ram? At best you have a few people on HN saying they're doing it, but in practice nobody actually does it.
ECC UDIMMs are crazy expensive, presumably because they don't have economy of scale. Mandating ECC would solve that.
Even before current RAM price craziness ECC UDIMM's were hard to find, and often more expensive than non-ECC. I was lucky to grab 128GB for similar price to non-ECC a few years back.
More people would use them, if they were available. RDIMM's do not work on normal consumer boards, so obviously people won't be using them.