Hmm, E-Ink doesn't need more battery life unless you're talking about the wireless or IR touch-screen drains. It is still an order of magnitude greater than, say, tablet PC's. Page turn speed is always nice but is the current generation an issue? I say no. Memory? Not a problem today, at least for those of use who avoid PDF's.
More than anything else I can think of, we need lower prices and higher screen durability. It will not be a mainstream commodity until readers drop well below $50 and don't break so easily. Color and higher resolution would be nice but the conversion of todays paper-based ecosystem will not become the dwindling minority until readers get both dirt cheap and child-resistant.