Although I'm not familiar with lithographic density, I do know that NAND has benefited from packaging improvements. Extreme back grinding allows multi-die packages (up to 16 for Toshiba), and the die are larger (over 200 sq.mm), so that "1000x" you see may be considerably less.
MRAM is much faster than Flash. Maybe it can be used as a non-volatile cache for solid state or even spinning-disk based hard drives.
Or even build a small hard drive out of it for the OS, for incredibly fast boot times.
Doing a "back of the envelope" calculation to compare this MRAM density to state of the art NAND, I get about over a 1000-times less density for MRAM. Granted, MRAM may have more scalability "juice" left in it while NAND may be close to the brick wall, but the old argument arises: are the benefits of MRAM enough to replace NAND in SSD?