Competitors/Alternatives, page-2

Intels Optane is the only Storage Class Memory (SCM) on the market. Link

Samsungs Z-NAND overlaps with SCM. Link

Optane is a Phase Change Memory (PCM).
4DS has a type of Resistive Ram (ReRAM or RRAM).
There is a few other SCM technologies coming up too - MRAM for example.
They all plug into the SCM market. Like Holden, Ford and Nissan, they do the same thing, but the details and way they're built are different.

The thing holding SCM's back right now is two fold.
1. A lot is still in development so there is no market for them, yet, because they simply do not exist (apart from Optane)
2. Even if more options did exist today, the underlying hardware infrastructure and protocols cannot fully exploit the potential. Most companies can get away with current technology for their needs (speed, power efficiency, retention)

Even once SCM's become more common, most companies simply do not need "persistency" of memory. It is estimated that persistent memory requirements is no more than 5% of the memory market today. Most memory requirements are find with SSD's or even Hard Disk Drives (HDD). Heck... Magnetic Tape Storage still exists today for niche storage requirements.

It will grow over time however.

It's a bit like trying to launch a smart phone app before smart phones existed... there simply was no current need for a company to have an app. It was not until after the underlying technology deployed to the world that apps were needed / commercially sensible.

Western Digital have demonstrated both PCM and ReRAM already. They have proof of concepts in-house.
They are just sitting on the technology because the market is not there yet. CY2022-2023 is the time I have been told when they will release these products. (I spoke with a Manager from Western Digital recently by phone).

Hopefully that helps.