I'm not saying eReaders don't make sense or that I'd refuse one. The world is moving towards eBooks, and although I elucidated several reasons why getting one doesn't make sense to me, it's nothing that can't be fixed. Got to move towards the future, you know?
But developers seem to be looking at the wrong things to improve on. So here are some things that would bring me closer into the fold.
1. Definition Lookup. This would let you click on a word, any word in the document, and bring up a dictionary definition for that word. It doesn't have to be much, just a little speech balloon popup. This includes foreign words, strange words, anything at all. If you want to go further, you could have Wikipedia lookup for some things. And even better, if spec fic books provided definitions for its jargon (Dune did this in the back of its book) or characters, in case you forget who someone is. Or even even better, those definitions could evolve depending on where you on the book.
For example, let's say you're reading Star Wars and you look up a Luke Skywalker on page 42. You see a brief bio containing information like that he was the son of a moisture farmer on Tatooine. Then on page 142, if you look at that character's definition again, you see all the additional stuff that's been uncovered, like that he's Darth Vader's son, he trained with Yoda in Dagobah for a time, etc. This is good if your character starts talking about some minor thing he did in the past that suddenly became relevant, and you forgot what it is.
2. No Videos, No Music, No Animation Get that shit out of there, I don't you need you mucking up my book. If I wanted to see a movie, I'd see a movie. If I want to listen to music, I'll choose my own music. You are an eReader, you're supposed to let me eRead, not eWatch. Take a lesson from the successful tech companies like Google and Amazon: do one thing and do it well. I don't want to download apps. I don't want to surf the web. I'm buying an eReader because I want to read.
3. Color (for the kids books) This is minor, and quickly becoming the standard, but I wanted to point it out. Kids are readers too, and my kids like the books with the coloriest images best. They like art, and they tend to like the same art as me--sharp lines, well-defined images, and whimsical illustrations. And maybe you could have some animation or interaction in those case. Just a little, because the point of reading books is ultimately, to gain knowledge from them.
3. Long battery life Here's the thing about electronic devices -- every time you charge the battery, a little of its maximum capacity goes away. It's why rechargeable batteries haven't taken over the world. So there's built-in obsolescence in everything you own. Not only would an eReader with short battery life get annoying after a while, but it would shorten its lifespan. And honestly, it does nothing but display text. It shouldn't be hard to make it power-efficient.
4. Text-to-Speech Capabilities (maybe) This would be a fun thing to have, to see how certain words are pronounced. Some say that it should be up to the reader, but I would have been able to lord something over people if I wasn't pronouncing it Herm-ee-own until the movie came out.
5. Reasonable Price That means features vs. prices. I already ran down my pricing model in that link up there (hardcovers bought per year vs. price of a kindle). But note the term "reasonable". That means the features it has should reflect in the price. If I'm buying more, something that will last longer, then it should be more expensive. If I'm buying fewer features, then the price should be reduced.