The prototype "robot printer" which Fuji Xerox are testing in Tokyo brings your prints right to the desk they were requested from!
Each office has a contactless card which is linked to a URL through which printing is launched. Once the file is dropped into the browser window, the print job is sent to the robot. The robot printer then starts to make it's way (using it's onboard 3D scan if the office layout) to the office of the person who ran the print job.
Once it arrives, the user presents the contactless card and printing starts.
Now that's mobile printing!