Every drone is uses a GPS ranging from position hold to way point navigation. But the performance of current GPS system has massive scope of improvement. Imagine a drone which can hold its position so well that its performance is comparable to a motion capture system's position hold and likewise for the way point navigation. 

I have implemented a monocular visual odometry on Nvidia's JetsonTK1. Using this implementation, GPS can be replaced with this camera based system. I dint have the resource to implement this on an actual quadrotor but I am quite confident that visual odometry can outperform GPS system.

Here is the blog entry for the implementation. 

http://www.robnsngh.com/2014/11/monocular-visual-odometry-using-nvidia-jetson-tk1-for-uavs/

Check out the actual implementation video from the creators.