They have this "holographic" optical disc tech that has a storage capacity of 1TB ... I think they already sell them or are trying to .... this tech does not have anything to do with holograms or 3D displays ... it just refers to how the data is stored on the disc or read from it.
I do not think magnetic hard drives will ever replace DVD or BD. The number 1 reason is that they are loud and always will be (even my fanless -- no fans at all -- external hard drive is louder than say my old DVD player, though not by much) and number 2 reason is that they, having moving parts, will always end up failing (law of physics).
What I am looking forward to should I live long enough to see it, is solid state storage. Imagine a future where an entire season's worth of the latest Showtime or HBO series was sold in stores on something resembling one of today's tiny USB flash drives. These would be very quiet, extremely reliable and durable, and take up so little space. Instead of having cases on a shelf, I guess you could put them in some kind of large key ring
They already have 64GB USB flash drives. Who knows what the future may bring.