Radio was supposed to make books obsolete. It didn't happen.

Television was supposed to make radio and books obsolete. It didn't happen.

Computers were supposed to make television, radio, and books obsolete. It didn't happen.

It is worth noting that that books, radio, and television have not become niche products either. They have changed with successive technologies, to be sure, but they are still fundamental parts of our society. I don't see why ebooks will fundamentally change this pattern.

(I also disagree with the LP analogy. An LP is just an electronic medium(1) for storing music, much like the 8-track, audio cassette, and CD. It is more analagous to the various ebook formats than print vs. electronic books.)

Footnote:
(1) Yes, I'm aware that LP's don't depend upon electronics. Yet most of the means of playing back LP's depended upon electronic amplifiers.