Custom centering hotkey: lean to the side (either with 6DOF headtracking or with the mouse), press the hotkey and your centered point of view now defaults to the new position.
That's all that's needed to be honest, not eliminating the view restrictions.
The reason we can't turn around much in gunsight view is that it corresponds to tightened shoulder straps. Judging by the now famous videos of the RAF pilot giving an appraisal on the 109 and Spitfire cockpits, it seems that having your shoulders tightly bolted on to the seat would severely limit a pilot's ability to look around: we only move our heads (at least those of us with hedtrackers) because we are using accelerated input/output curves in the relevant interface, but in reality to look back one needs to turn the torso around as well.
Anyone who's driven a car and had to reverse at some point or parallel park knows this, to look back you need to turn the entire upper half of your body around and not just your head.
This is what the gunsight view simulates first and foremost, with the straps tightened there is less headshake at the cost of reduced ability to turn the our virtual body around, with loosened straps we can look back easier but there's more headshake.
That's why i am firmly against eliminating this feature:
1) It's realistic.
2) The gunsight troubles are a side effect that can easily be fixed.
How? By making the reticule visible from the normal centered position (to simulate the fact that in reality our right eye would be able to see it) or giving us the ability to set a custom center viewpoint.
There's no need to do away with a realistic feature just because of an easy to fix side-effect, it would be like disabling the mixture controls on RAF aircraft because they are reversed: "this is confusing, let's completely delete it instead of properly fixing it", it's a throw the baby out with the bath water approach
