Hi Tom (@TomBarwick ),
The L1 Navigation never made it into master however there has been some work done to improve the turning in copters’ auto mode. In 4.4, a new parameter was introduced that can be used to minimize the speed lost in corners. Here is a post by Leonard that describes how to do this.
I have played with this new parameter and it does help. I have not fully explored it though.
If you have any questions, you can post here or you can post directly on that thread. Be sure to tag me if you post there so I am sure to see it.