Customizable FOV has been addressed in other tickets, what I would like to address is the continuity in vehicles.

If you sit in a truck or quad-bike as driver and zoom out, you get an extreme fish-eye FOV. This might be for situational awareness, but this affects the mouse sensitivity (makes it faster thus jumpier) and affects the experience (causes a bit nausea for some).
As a passenger you can zoom out only slightly bit, almost no difference.
The default FOV for the little bird is actually nice, but is totally different for a passenger.

In short, the default and other FOV's should be same, always, everywhere at any time.

Zooming out should not have an extreme zoom out, so if you feel the default FOV is too narrow for that vehicle ride, than zoom out, but the FOV should be same as when you're a soldier standing around. Preferably of course if you could set the FOV to your liking.

The zoom out should also be reliable, it doesn't work permanently in most vehicles, you need to hold the key even if you double tapped the zoom out key to toggle to the zoomed out state.

Also, the level of zoom resets when aiming sights. FOV/Zoom should be adjusted and aiming sights should not reset it, unless you set it up like this.