I have just duplicated the kinect.urdf.xacro file and replaced the mass with a lower number and than added the following to the erlecopter.urdf.xacro:
<xacro:include filename="$(find ardupilot_sitl_gazebo_plugin)/urdf/sensors/kinect-custom.urdf.xacro" />
<origin xyz="1.6 0 0.55" rpy="0 0 0"/>
where kinect-custom is the modified file. I get the ros topics, but did not manage to get any SLAM algoritm working properly. I am not sure if it is due to bad configuration or a wrong approach with the kinect.
I am just testing the functionality of a depth camera, I'd figure out that if the kinect would work, there are other (lighter) depth cameras that would work too.