I doubt we will see throw away ebook readers.
Two points. First, I doubt everyone will agree on an interface. Heck, in the audiophile world there are still people who listen to music on records with big old tube based receivers and swear that it's the absolute best sound available. I suspect there are some who wish they could get all their reading material via illuminated manuscripts.
Second, I suspect that as more and more people grow up with smart phones and tablets, reading on such devices will be second nature to them. I see toddlers who are comfortable using an iPad. It's pretty hard to guess where we will be in 20 years.