It's not just Optane. There have been other NVRAM technologies that were hyped as "fast as SRAM, persistent as HDDs, cheap and dense as DRAM" over the years such as FeRAM and MRAM. MRAM exists as a commercial product but it still fails to deliver on the cheap/dense part.
FRAM and MRAM have found a place in embedded markets doing weird things - MRAM is a low-cost alternative to space-grade flash right now, and both FRAM and MRAM are used for small, fast persistent "caching" with good wear-out. Optane was the only one of these products that was really targeted at the server space, and had much better density than FRAM, MRAM, PCM, and all the other weird alternatives.
