Novel hardware technology usually is introduced to overcome shortcomings of established technology but nothing is free in live so the novel technology usually has shortcomings of it's own which need to be accommodated in system design. For example, we're looking at a wave of Non-Volatile RAM (NVRAM) technologies - Flash memory being the best known but others such as Phase-Change Memory (PCM), Ferroelectric RAM (F-RAM) or Magnetoresistive RAM (MRAM) - sweeping in to replace established DRAM in embedded devices. This happens due to the relatively high power consumption of DRAM which needs to be regularly refreshed if no write operation happened within the last time frame. Contrary to that, NVRAM - as the name suggests - retains data even after power loss, removing the need for power consuming refresh operations.
However, these novel NVRAM technologies all have one major draw-back: after a certain number of write operations, they will invariably fail. Due to this, wear-levelling techniques that map logical addresses to pseudo-random physical addresses in order to spread write operations over the entire physical address space, ensuring that all memory areas have approximately the same life time. Of course, would cryptographic memory protection interfere with wear-levelling or incur additional write operations, that would be a bad thing. But do we need cryptographic protection for RAM memory? After all, we have lived happily for decades with unencrypted and unauthenticated DRAM. (Except maybe a few special cases where encryption and authentication was necessary.)
The authors of " An Efficient Run-time Encryption Scheme for Non-volatile Main Memory", Xian Zhang, Chao Zhang, Guangyu Sun, Tao Zhang and Jia Di raise an interesting issue: Cold boot attacks on unencrypted RAM become a lot easier if the RAM is non-volatile; NVRAM does not loose it's information and hence the "cold" part of cold boot attacks is not required any more. Basically NVRAM behaves similar to hard disks and several information leaks due to lost or stolen laptops have highlighted that hard disks in mobile devices should be encrypted.