According to the article, current high-end drives have densities at around 120-140Gb per square inch. This would make the new tech about 7-8 times as dense.
If we assume that a modern 400G drive has platters at the 120-140Gb density (a reasonable assumption, although I don't know for sure), then this new tech would produce a 2.8-3.3TB drive.
And if we want to be silly about it, an XServe RAID chassis loaded with these hypothetical drives would have a 40-46TB capacity. Of course, that's just silly-talk. For now.