My dream e-textbook

In 2010 when I first started writing and presenting on e-books, I was asked to review an e-book reader for use in schools by a tech company. It was a standard e-paper type reader, similar to an early Kindle or Kobo. I concluded it would be good for fiction texts and maybe History, but not for a subject like Maths or Science, where you need to flick back and forth between examples and questions.