...that I have been thinking about for a while now.
Increase the amount of updates per second of aircraft on multiplayer, to allow for fluid MP aircraft position updates.
And, building on that, allow the ability to have more than one person flying the same plane over the internet. At least allow a copilot, even if they do have to use the same panel. Ideally, on a default plane, each person would just see the left side view (trying to minimize extra work by the MS team, you don't have to create a right seat view for each airplane). However, both pilots would be able to manipulate switches, and perhaps include a little utility to allow either pilot to fly.
Then, in payware addons such as the LDS 767, which includes a right seat view, either person could choose whichever side panel they want (left seat or right seat).
Also, possibly allow even more people to be in the VC of the aircraft, maybe do seat assignments like in Battlefield 2 (Each vehicle has multiple seats, with different spots in the "VC"), allowing the possiblilty of online "passengers" in our flights.
This would be useful for people like myself who enjoy flying the heavies, and also since I am the Training Director at my VA, it would make teaching people how to land a lot easier.
Microsoft, please consider these ideas. Thanks!