Having rather painlessly installed ROS Indigo on El Capitan using Mike Purvis's script, I attempted to upgrade to ROS Kinetic. This gist outlines the problems I encoutered and how I solved them. Hopefully this guide will help others attempting to install ROS Kinetic / Gazebo 7 on El Capitan.
Start with Mike Purvis's script, which currently is setup to install ROS Indigo. In order to install Kinetic instead of Indigo, make sure to set the ROS_DISTRO environment variable: export ROS_DISTRO=kinetic.
After you get through rosdep errors, it's quickest to just work with the catkin config ... and catkin build ... commands directly. In fact, I found it most helpful to leave my catkin workspace terminal open at ros-install-osx/kinetic_desktop_full_ws and then opening a new terminal to go tr