I don't know how long it will take but I think there will be a point in the future where a limited number of books will actually make it to paper form. Those will be collector type books and hopefully of a much higher quality than today's current popular fiction books that lose their glue after 3 years. I really don't see much of a market for MMP in the long term. People who buy paper will want quality.
I also foresee the role of individual agents morphing. Rather than shopping a manuscript around to Publishing houses I think many of them will start to focus on connecting chosen authors with good editors, helping them format digital books, and then marketing the books to the public and providing the files directly to retailers. Branding will be done through Agency ... with the big names developing brands and reputations for finding the "Best Legal Thrillers" or the "Best Paranormal Romance" etc. The authors and their agencies will then split the commissions - largely cutting out the traditional publishers altogether.
In short .. there will be some agents who become the gatekeepers of what what we want to read, rather than traditional publishing houses.