This game will define immersion. I know it'll be great. Wind, fire, trees, (character) animations, physics all top notch. And large environments to explore, finally. Superior gameplay to Crysis linearity, no doubt (better looking even - don't use parallax mapping or advanced stuff like that, keep things simple). This is my kind of game, and it's hard to come up with ideas to include (except for rope climbing/swinging maybe).
But I very much want to see a motorcycle vehicle (jumping over hills) and a helicopter (similar to the one in GTA:SA near the dam, with the glass dome cockpit). Please include these. (Daktari).
The hang glider can not replace a heli. A heli doesn't lose altitude quickly, and has mounted guns, or at least it can.
I think they should look at adding a dirtbike, since obviously a street motorcycle wouldn't work. It makes sense that someone might drive one to a military camp in Africa, since they're small, fast vehicles. I have a KX-125, and it goes pretty fast. Maybe add some 250cc 2-strokes and 500cc 4-strokes.
I don't think we'll be able to fly helicopters. I remember reading in an interview where one of the developers was bragging about the vehicles in the game: motorbikes, trucks, ATVs, jeeps, buggies, hang gliders, yet he didn't mention helicopters. Don't you think helicopters are something worth bragging about?
Unless they make them as a last-minute addition, I don't see them happening. I would bet that the enemy flies them though and you will have to take a few down with your RPG.