Most kinds of memory devices are based on old principles of making a memory device, which are applied to new materials.
I do not think that any new memory device principles have been invented after WWII. Already by 1940, the inventor of DRAM, John Vincent Atanasoff, had enumerated almost all principles that can be used to make a memory device.
The first DRAM of Atanasoff was made with discrete capacitors, then 5-years later von Neumann proposed to use iconoscope cathode-ray tubes instead, which were used for a few years, before being replaced by magnetic core memories. The Intel company was formed for the commercialization of the first (1-kbit) DRAM integrated circuit made with MOS transistors.
The memory described in TFA is in principle equivalent with a memory made with mechanical toggle switches or latching relays with mechanical latching, where the 2 stable states are maintained by elastic forces and you can toggle the state if you apply a force great enough on the switch.
Reducing a mechanical bistable device to the size of a few atoms reaches the possible limit of memory density. As described in the parent article, this device should be able to store information safely and it should be able to switch is state quickly.
The difficulties are not in the memory cell itself, but in how to enable fast and accurate reading and writing. While the memory cell itself may have the minimum size permitted by the atomic structure, there is no way to miniaturize to the same extent any kind of reading and writing interfaces, so that they could be incorporated in the memory cell, like in an SRAM cell.
Therefore the only solution that can preserve the high cell density is to have a read/write head that is shared by a great number of cells, i.e. which must be moved in order to access different cells.
So the memory, at least within some block, must have mechanical access, so it must be implemented as a tape or a disc. Multiple heads could be used to increase the read/write speed, like also for magnetic memories.
So I do not think that there is much to criticize in this paper, it makes sense and it identifies a new material that is suitable for implementing a known kind of memory cell at an atomic scale, even if it is unlikely that a practical memory based on this concept will become possible any time soon.
Microsoft has worked for many years on their glass memory devices, which have much more important advantages, and they are still far from being able to sell such devices, mainly due to the cost of the required lasers, for which there is a chicken-and-egg problem, they are very expensive because they are produced in very small quantities and they cannot be incorporated in a device intended for mass production, because they are too expensive.