Here is a dual extruder solution from 3D Proto where a non-printing extruder is parked outside the print area to prevent oozing which gives better print quality.
When a idle extruder is parked outside print area it also gives higher speeds and movement precision to working extruder. It also prevents possible scratching of one extruder on the printed object.
Very interesting solution.
There are some possible limitations on x-axis due to the width of assembly but it is maybe a minor inconvenience.
Project homepage where more information will be published (with build instructions hopefully):
Here is explanation of parking dual extruder and video of it in action: