Concentration spans are diminishing worldwide - what does this mean for books?

According to the Guardian article Got a Minute?, global concentration spans are diminishing worldwide. There are more things grabbing our attention, but less attention to grab.

What does this mean for books? Should they be shorter overall? Dumbed down? Shorter sentences? Shorter words? What does it mean for a person's ability to think and focus on one thing?

Here's the old question back in a different form - should I write what I want or write what I think people might read?

Write what I want, of course, but I do have to take account of how to get and keep my reader's attention. Margaret Atwood said that was all there was to it - just get the reader's attention and keep it.