Hi David,
Thank you for the effort you put in. Honestly I do not know about your specific contribution because I do not use the navigation stack.
Robots work in a 3D space or even in 4D(with time constraints). As far as I know, the stack is not designed with this in mind. Correct me if I'm wrong.
It is not necessary to have all algorithms in place, but having a general navigation architecture encourages more people to adopt it and contribute 3D algorithms. Consideration for robots models beyond differential drives are also useful.
Regards
Aswin