Couple of part ideas I'm wondering if they're in development or not.

Flaps: In the real world flaps are a control surface that sits on the main wing close to the fuselage. At low speeds the flaps are extended and pointed down to act as a combination airbrake and to increase lift. This doesn't necessarily have to be a separate part but the option to control a second set of ailerons through the VTOL commands would be nice.

Turbo Shaft Engine: This is the kind of engine that typically used in helicopters. In the case of the game this would be a horizontally configured (weight wise) turboprop engine with a vertical drive shaft. The reason for this vertical drive shaft over simply pointing one of the existing engines upward brings me to my next subject.

Cycling Pitch: This device sits between the engine and the rotor on helicopters. They work by changing the angle of the rotors to move the helicopter forward, backwards, and side to side. With the current parts you would have to build a complicated (and more importantly, heavy) system of rotators to simulate this. Having cycling pitch would make the tilt-rotor I'm working a lot easier to control.