In twenty years, your average $50 ebook reader will have a 300 dpi full-color full-motion transflective screen, readable in sunlight or with a backlight. Most of the weight will be battery. It will have a tiny CPU and a relatively studly GPU, a small amount of permanent storage (less than a terabyte) and a short distance wireless network link, which will feed your headphones if you want sound, or connect to your phone or your house networks.
There will be a secondary screen on the back which displays the book's cover. You will have the option of changing that to anything else you want to display.
Many people will not bother to buy them, because they already carry a phone that can do all that, just with a smaller screen.