Main problem with Sun is that you can turn camera directly into it and watch that white ball like any other star or Moon. But in real life looking at Sun is possible only at sunrise/sunset position.
I am wondering, is it hard task to add some interaction like smoothly whitening all sky around Sun when camera is watching directly into it. Also cockpit inner illumination should change its brightness during that moment (to became darker but with light glow on the cockpit window edges).
Sun outer glow and its appearing through clouds also should be more increased because sometimes its very hard to find it behind clouds, but in real life it differs.
Lens glow effect also should give + to realism, I think.