I'd like to have a tool option to place one, or multiple markers at any location with or without an object at that location.
The ability to enter arbitrary reference markers with a mouse (e.g. control-click) and/or a script (boolean true/false option within a move-to command) would be very handy in my opinion.
I often us the angle tool to measure differences between an object's actual position and predicted/reported position. It would be very handy to have a marker to reference to and not disappear when I click an object. I currently zoom in to find the nearest star but it's not exact and disappears if I click another point (when not in angle-measure mode).
Having "free" reference markers are also useful for graphing (and tracking) multiple object positions on the same screen. For example, asteroid/comet/satellite orbit positions over time.
Bottom line, I think user-created "free" reference markers would really boost Stellarium's interactive graphical capabilities for problem solving, prediction and exploration.
Please check version 0.90.0.8715.
Hint: Shift + Left Click/Right Click.