The idea of putting ssds in memory dimms isn't new, the jedec standard for this is included in ddr3. It's referred to as an nvdimm(-f for SSD), sandisk and IBM both produced and sold them. These are supported since Linux kernel 4.1 and show up as a block device in /dev/pmem. The latest optane variants are nvdimm-p and are not treated like block storage devices but instead as persistent memory to the OS.
The storage dimms have some notable benefits over pcie nvme ssds - latency to the processor is extremely low, they give extra total storage I/O since they're leveraging a different controller on the cpu with its own bandwidth, while still leaving pcie bandwidth for traditional storage. They can add capacity to a small system (a 1U server can hold 24 such ssds)
As I see it though, these optane dimms are just fast swap drives which do not offer the same consistent throughput as true memory dimms. They are transparent to the OS which is normally in charge of deciding what stays in memory and what goes to swap. Use of an Intel sdk is required to leverage much of the benefits. It's also Intel-only as far as support goes for now. As usual the marketing doesn't mention the throughput or pricing and instead of comparing to memory they compare it to storage.
http://www.admin-magazine.com/HPC/Articles/NVDIMM-Persistent...
https://thessdguy.com/an-nvdimm-primer-part-1-of-2/
https://www.extremetech.com/extreme/270270-intel-announces-n...