As Mr Barnes pointed out, if the physical book is to resist the challenge from the ebook, attention to the former's aesthetic factors should be taken seriously. Size is part of this. The pleasures of the Kindle, for example, are inextricably linked to its convenient size. Authors should take note. The 1,000-page blockbuster or the door-stopping biography work better as ebooks than in printed form. For the physical book, therefore, the future is surely shorter.
My kindle is the same size and weight regardless of whether it contains 1000 books, or just one small article.