Well who are the competition? The only thing close is World Of Planes as they are in the same time period. So what would make the WOP guys squirm?
Maybe something to bring in the 'aircade' players?
As we are on Steam maybe it's all about hats, like in Team Fortress 2.
http://tf2wiki.net/wiki/Hats
We get to collect hats and trade them with other players!
The open canopy aircraft will be all the rage because other players will have unrestricted view of our magnificent hats. Oh the jealousy!....