What has failled to be recognised in this thread is the vast majority of the increase is because to hipsters. You know, the kids who are into records because they're "trendy" or "retro" more than appreciation for the technology. Personally I dumped about 85% of my LP collection a few years ago because I already had the bulk of them on CD (factory-pressed), I needed the shelf space and was getting increasingly sick of hauling those stupid things around. 45s, of course, are garbage to begin with so I at least didn't have to worry about getting rid of any of those.
The present "comeback" if it can be so called of records is a fad, like 3D movies and that "paleo" diet. It will die out in a couple years once the hipsters start trashing mini-disks because they think they're "retro".
Dual Disk was tried some years ago and as far as I can tell, it failled miserably. Not only did they really not bring much added value to the market but since it had to violate several aspects of the red book standard in order to be what it is, it introduced a rather dizzying amount of compatibility issues to the format. Not to mention the "special" storage boxes they often came in were a major PIA to get open without breaking them in some way or other.
I don't know how a double-sided CD (both sides CD like-CD like) wouldn't introduce the same problems the previous attempt did. The industry would have to have either a masochistic side or just be really bloody stupid to deliberately repeat that technological blunder.