I have no idea where on those slides it says non-volatile storage should not be used for non-permanent, temporary data.

It does note main differences (speed, latency, permanence). How does that limit what data disk can be used for?

What would one use optane DIMMs for?

Also, if my program requires huge working set to process the data, why would I spend the effort and implement my own paging to templrary working files, instead of allocating ridiculous amount of memory and letting OS manage it for me? What is the benefit?