1) 3D buildings in the flight sim. I understand that some people's connections are slow, but it's a pain to turns on the buildings every time I want to see them in the flight simulator. Just make it so you can set 3D buildings to automatically be on.
2) Some new airplanes. The F16 and SR22 are nice, but I want more:
2a) How about a WWII plane? A Supermarine Spitfire, P51 Mustang, or Zero would be cool, for more altitude and speed than the tiny SR22 but similar low-speed landing and maneuvering capabilities.
2aa)This also raises the question of dogfights, Air-to-air missiles, and even bombing in Gearth.
2b) How about a 747? Nice for when you want decent speed, altitude, and landing abilities, plus a challenge in landing a big plane on the runways.
2c)Ideally, though, I want an SR71. Mach 3 speed, 100-mile-radius turns, and 90,000 foot+ max altitude. I want to be able to go places fast. If they can program in the 'dipsy-doodle' maneuver (dive a bit to get through Mach 1, then push the nose up and climb very, very fast), then that would be great.
3) Speed control is a pain, especially for the F16. Afterburners (for 1400 mph flight) and speed brakes (for landing) would be very helpful.
4) Some sort of autopilot. The  button to center the turn and roll surfaces helps, but it'd be nice to have a function that automatically kept the plane in a straight, flat line if you hit it while in stable flight. Someone outside Google ought to program a terrain-following system. Now that'd be cool.
5) Navigation. At very least, a compass so you know what direction you're going, but preferably a little screen with a downwards facing map.
Just a few ideas.