I know that for now, tape wins versus optical (Blu-Ray Recordable etc.) in terms of cost.

Do people expect that to always be the case, or is anybody expecting tape to have been supplanted by something else (optical or other) 20 or 30 years from now?

Or is there just something about the physics of tape technology that we can't even imagine anything else in the medium-future that could even begin to compete with it for archival needs?

(Knowing nothing about the area, just as a consumer I would have expected that with the advent of 2-layer DVD's and then 4-layer Blu-Rays, that before too long we'd be getting 1,000-layer discs and essentially moving into 3D storage cylinders by now or something that would have left tape in the dust...)