Before letting lengthy encyclopedia articles which might distract you from your reading inside the thing, there is something with more potential of convenience and, in general, more WIN, which still hasn't been even rumored to be included in readers: technical dictionaries and glossaries.
I can picture many an economist having an orgasm if s/he can have
the Palgrave dictionary in the tip of his/her fingers, and M.Ds could make great use of their vademecum books. Now THAT would be a big leap forward.