Consumers were always capable of disabling it themselves if they didn't need it. The performance impact seems to be ~3% on average, impact on power consumption is probably similar or less since any extra delay idling can destroy performance while not having as big impact on power consumption. https://www.phoronix.com/review/amd-memory-guard-ram-encrypt...

Any extra cost would be mostly due to power consumption and testing that the feature works (which they probably don't do for consumer skews anyway). The area of silicon used by the feature is probably negligible, from the manufacturing cost perspective it's cheaper to avoid any unnecessary design differences between skews.

Despite it being hardware accelerated I've always wondered what the energy cost for HDCP encryption on HDMI connections is.