You'll notice that we have at least three filesystems (tmpfs, procfs, and sysfs) which don't use anything other than RAM. You'll also notice that programs make extensive use of filesystems for the well-specified inter-process semantics around the common case where the computer doesn't lose power and RAM keeps working.
Oh, and we use filesystems for disks, which NVM doesn't replace, not for DRAM, which NVM does replace. It would make more sense to say that now we can now have *only* filesystems, not anonymous memory. But that's also dumb.