Really what has multiplay got to do with a simulated aeroplane flight? Plane to plane interaction is avoided like the plague in real life. A two seat cockpit interaction might make some sense. Perhaps the I. Flight or Sky Gamblers: Storm Raiders fans would want it but would it make enough revenue to cover the development and maintenance cost? I wouldn't pay anything for it.
Is multiplay some sort of a social media gaming thing? is it for military formation flying? what?