@Grozzie,
Optane (AKA 3D XPoint) is not your typical NAND flash technology -- most certainly not stacked planar NAND (e.g. like Samsung's 3D V-NAND).
It is non-volatile RESISTIVE RAM (ReRAM). This is only the first ever generation of ReRAM technology that has been made available commercially. THIS IS A HUGE BREAK-THROUGH.
ReRAM, Phase-Change RAM (PRAM), Memristors, and CNT RAM has been worked on, at least in high gear, for well over ~5 years now. If you look into this, Micron, Intel, HP Enterprise, WD, SanDisk, Toshiba, Samsung, and Seagate have been contributing....but none of them really gone past lab testing stage, except for ReRAM in the form of 3D XPoint.
According to the now recently disbanded ITRS 2.0 (International Technology Roadmap for Semiconductors), we are nearing the physical limits for silicon-based memory technology. Most NAND / DRAM technology are on ~20 nm, and the projected limit is 15 nm ~16 nm with silicon. 3D XPoint (along with emerging Carbon nanotube (CNT) technology) is capable of scaling down below 1X nm. From speculations (since Intel is keeping specifications to themselves very tightly), first generation 3D XPoint is on 22 ~ 20 nm lithography.
I won't be surprised if second or third generation of 3D XPoint (or QuantX) can achieve, or surpass, DRAM performance while being non-volatile.