Companies like Seagate Technology and Western Digital believe that to hit areal densities beyond 1.5Tb/in², HAMR technology along with higher anisotropy media will be required because of supermagnetic limit (physical "pitches" on optical [sic] media become so tiny that it will not be possible to produce a powerful enough magnetic field in the HDD space to write data into them).
Certain principles of heat-assisted magnetic recording were patented back in 1954, even before IBM demonstrated the very first commercial hard disk drive.
The problems now faced are not science, but engineering. Of course, lots of those bytes are never recorded if/when developers embrace Organic Normal Form™, and reduce storage footprint by an order of magnitude or so. And get DRI. And so forth. Someday my Prince will come. If only he weren't so damn drunk.