Encrypted RAM as AMD is implementing it (SME) protects nicely from "cold-boot attacks" but is otherwise largely a feel-good feature. It also probably doesn't help a whole lot against rowhammer-style attacks because it's merely encrypted, not authenticated. The result is that a bit flip will effectively randomize 64 bytes or whatever the block size is but will not be otherwise detected by the hardware. I bet that clever attackers will find a nice way to take over by randomizing 64 bytes.

Intel's encrypted RAM is authenticated quite nicely, but it's not (yet?) designed for general purpose use -- it's for SGX only right now. Using it for everything would (if I understand correctly) add considerable space overhead and possibly considerable latency.