I don't see how that solves this problem. there is a string in memory that gets saved on suspend. that string when read by the CPU has the same properties it had before. if the CPU is using rot-13, the string is still rot-13 and the attacker doesn't need to spend the compute needed to crack rot-13, the CPU will simply do that as normal.
Memory encryption is secure under a certain threat model. It makes cold boot attacks, DIMM transfer attacks, and rowhammer much harder to pull off. It doesn't protect against everything and doesn't pretend to do so, but IMHO it's valuable anyway.
