Some combo of flash and spinning rust storage really makes the market for very high capacity optical storage a bit niche. It might still have a place as archival media (and multi-layer optical disks, which are 3d optical storage of a sort, though not to the level of sophistication imagined in the 90s, are used in that role to some extent), but it's just really hard to see it rivalling flash for mainstream applications at this point. In particular, flash is really, really, _really_ fast.