I think we're *eventually* going to wind up with a unified memory technology that flattens the memory space, but I don't think Optane is it.
When this was first a thing, the Optane access times were a couple of orders of magnitude off RAM. It really read like a newer/better/faster version of existing flash storage media. Of course the critical thing is "Can you make it price competitive with existing NAND?"
If they can't, it's going to be a tough sell. Existing NAND storage has gotten to be fast, durable, cheap and is growing in capacity. While you *can* use faster storage in front of slower capacity storage as a cache, existing NAND is so cheap now that everything is migrating to flash.
Caching works, but it's complex and has overhead penalties, which is one reason why all flash storage has grown in popularity. The consumer wants one drive, not two, and even the enterprise wants speed and simplicity.
I'm curious what Intel's problem is. Is it just an early production capacity problem or are their yield problems? Or did they drink their own kool-aide and think that people wanted to step back to multi-tier storage for their new cache chips?