I have an interest in zeppelins and other airships and I think it'd be really awesome to include airships into this game. Afterall, y'all did add cars and such, so zeppelins shouldn't be to far of a stretch (I hope).
This could be implemented similarly to bouyency and dead weight, but instead with an adjustable amount of either hydrogen or helium.
Another thing to consider could be docking hooks for those airships, so we could launch planes from them. Just a suggestion, and I hope this will be considered in the future.