Only a stopgap until everything is NVRAM, and then all this half-way technology will become obsolete.
I can't think of a single reason that NVRAM can't replace all current RAM and SSD storage in time, or why you would not want it to?
So long as you have a button that allows a "memory clear and boot" if you ever really need it, I think it's a no-brainer.
Like USB flash drives being used as "fast cache" for the storage devices of old, or hybrid SSD drives, it seems like one of those technologies that will only obsolete itself if it gets popular.