/upvoted

I really like the idea. You are forced to manage your inventory. Drivers will stay drivers and pilots will stay pilots. But I don't think, it's in the interest of the casual gamers.

This is the only problem with it, perhaps it would be a module configurable from mission to mission

For MRAPs and trucks, no, as the crew is likely to be forced to disembark, but for jets and other vehicles with limited/no cargo space, yes please. Upvoted. Pistols and maybe SMGs should be allowed though in my opinion.
Edit: Having it as a parameter setting would be a good idea I think, just like dropping weapons when swimming in Arma 2.

I'll update the "additional information" to more specifically describe what slots would get what

Upvoted!

Upvoted!
There is a vehicle inventory for reason and also it should reduce the one man rambo style gameplay.

With the ability to access inventories from inside vehicles, I don't see a problem with this as it could be scripted into forcing you out of the vehicle as you grab your weapon.

Either that or simply do not allow the person to put the weapon in the slot (as if you were trying to put a rifle in the pistol slot). I think forcing them out is a little unreasonable.