Hello,
I'm glad to hear there is some interest and work going on with the ROS navigation components. We decided to build our own internal nav package due to a few things not being available at the time we looked:
1) Flexibility in bringing in measurements in different ways (loose integration, tightly coupled,...). For example, camera measurements can be brought in to a filter via PnP, raw non-linear angle measurements, as a velocity update (odometry), and so forth, each with their own advantages. We wanted a way to generically specify the sensors and then have the filter bring the measurements in via a configurable option.
2) Easy plug-and-play sensor swapping. For example, being able to add in
an inertial to an already existing lidar/camera navigation filter and
have the filter automatically convert itself to an error-state model with respect to the
inertial; ideally, without having to change any filter code (only bring a new ROS
sensor node online).
3) The ability to apply to quadrotors and other 6dof applications.