In a December letter to the SEC (recently made public), Google makes some interesting predictions about the future of advertising.
Another interesting statement reads:
The shifting nature of mobile may be why Google is throwing so many darts at the board (think wearables like watches, glasses, etc). Clearly Google is struggling to find the next category of mobile devices that will help drive its advertising revenue. It understands that missing the boat could be a catastrophic misstep for the search giant.