I think the main benefits would be rethinking the core of persistence to be more about atomic operations on datastructures as opposed to POSIX filesystem IO.

I personally believe that files are still a useful metaphor, and this hypothetical OS that we're discussing would likely still provide them, at least for interop.

An example being a database. Provided we didn't have to batch writes, be aware of dirty pages, write things in certain order to maintain coherence in the event of a crash, etc... we could build something really simple. Ultimately it would depend a lot on the details like memory bandwidth+latency between DRAM and NVRAM