zodiacfml :
HAMR, as mentioned already, can scale at higher capacities. Light simply has a smaller wavelength compared to microwaves.
You're missing the point. The lasers/microwaves aren't use
write the data, but rather to reduce the coercivity of the recording media. Consequently, the area heated by the laser or affected by the microwaves can be larger than a single track.
zodiacfml :
Flash has a better future though where these HDDs will replace magnetic tape drives.
"better future"? The challenge for flash would be merely to keep up with the density improvements of HDDs. We're already in a world where you use flash for speed and HDDs for cheap nearline capacity, and that won't change for the foreseeable future.
BTW, I doubt even these HDDs will offer the cheapest offline storage solution. Anyway, 100 GB blu-rays are a true archival medium, if not also the cheapest per GB.