I'm utterly unqualified to discuss using it in practice but it always seemed like PMEM would have required a fundamental idiom shift away from the DRAM concept.

If you treat it like memory it's always going to be slow memory. If you treat it like storage, it can be very fast storage. If that makes sense.

Software that "treats storage like memory" would end up looking a lot like javacard imo. Or something like Samsung's in-memory key-value database stuff. But it wouldn't really look like a linux kernel allocating memory inside an all-pmem partition.

Difference, in my head, being that essentially the filesystem is an unnecessary layer/abstraction in the middle. You want something that either looks like a garbage-collected runtime, or an in-memory database that vacuums, or LISP collections of object-trees, etc.

There is no point to having a separation between memory and disk anymore, that is the point - "resource allocation is disk persistence" so to speak.

It would have required a big-bang rewrite/second-system that is just not possible with the dominance of the existing RAM/storage dichotomy. Or at least a couple killer apps from large vendors/etc that really outperformed what was possible with RAM.