Interesting story in Overhaul and Maintenance Magazine. WheelTug is working on a self-contained powered nosewheel steup for the 737. The vision is self pushback and ability to taxi without using the engines. (the APU will provide the electrical power for the unit). Here is the link to the company:
http://www.wheeltug.gi/index.shtml
http://www.wheeltug.gi/index.shtml