So I bought the game the other day, and so far, all I can say is that it has me excited for even more content in the future. Some things I want to suggest are the following (lower priority first):
1. Custom soundtrack support
-Although the soundtrack in the game is great, lots of flyers I'm sure would like to have the game support their own musics. Yeah you can always play it in the background but it doesn't always have the same feeling of a real custom soundtrack.
2. More aircraft customization
-I really think that the game lacks a bit in the department of aircraft customization. For example, unlocking special parts; there are only four, and the system isn't like that of, say, Need for Speed or Forza Motorsport, which provide numerous options to customize your vehicle. Heck a paint editor similar to NASCAR 14 and Forza or a template based import system would be cool, too, but inappropriate aircraft would definitely be an issue.
3. More aircraft
-Currently, we've got four planes, one which is a Cessna, another an Extra stunter?, then a historic I-16 lookalike, and a mystery plane. My suggestion would definitely be to add more aircraft into the game. Be it WWII reproductions (what I REALLY want to see, would LOVE to fly a P-38 or P-51 lookalike!) or just stunty takes on modern prop planes, three aircraft just isn't enough in my opinion.
4. A few more locations
-As of now, the game has a desert and a forest-like map. To me, even though waypoints can be placed anywhere, there just isn't enough variety in the locales. For example, you could include locations such as a Tuscany style type of map, or a tropical archipelago resort, or get creative and go for crazier areas like a volcano, a city, a giant air racing arena, THE MOON (okay maybe not that far but you get the point :P).
Anyways those were my few suggestions. I know it's probably asking a lot, but this game has a lot of potential.