Default Game controller overlay

With all these game controller enabled games and gamepad embedded tablet, how come there isn't any LMT type controller overlays to emulate , lets say, a xbox controller? You would have the option to play limelight with just your phone and no wires or phone props. You wouldn't have to adjust between different controller overlay styles. Some apps even charge just for having the feature added but only to their app. (splashtop) Seems like there is a demand for it just know one seems to know it.