Digital signage and personal digital displays

How long before digital signage as the primary medium becomes digital displays that augment, or are secondary to personal / mobile displays? I think it is happening faster than we think and it is coming from a wave of technology that today has nothing to do with what we have traditionally called the digital signage industry. Twitter acquires geo-enabled API provider Mixer Labs

Instead of the "where" of the tweet "earthquake" how about "at the mall", "hungry", "at office", or "looking for a blue dress" and the mall map becomes available to guide you to what you want and the stationary displays show where you are, restaurants and their specials near you appear and greet you at the door - and they know what you like, the office informational displays greet you and show you the metrics you are most interested in before returning to their standard loop and photo's of blue dresses that are available near you and for order over the web scroll on by on your phone.

For those that fear the new order and have privacy concerns - it's all on an opt in basis only! No minority report retina scans!