It's definitely possible, but we may have to go through a lot of code to allow a negative thrust.
I think the harder part is figuring when to effectively apply the reverse thrust.
There are also other ways landing could be optimized. That glideslope angle corresponds to a given airspeed for your vehicle. We could have additional phases where you descend faster (steeper).
Setting up landing is really 2 waypoints. The actual LAND, and then the previous waypoint to line up the approach. One thing you might want to try is using MAV_CMD_NAV_LOITER_TO_ALT as that earlier waypoint. You can use this to descend in a tight loiter, then exit the loiter on a tangent when the heading is aligned towards landing (params #1 and #4).