As I've already mentioned I found a way to add roll inertia, the game engine seems to accept it without a problem, but after a few test flights I don't feel I like this effect. Maybe I just did something wrong, or maybe it is the way my brain reacts to rotating image, but so far I think the roll should be minimal and definitely optional.
I think optional would be perfect. Certainly some folks wouldn't want the added challenge of roll when trying to aim. Speaking for myself, I feel like it adds to the difficulty in a natural way. Sure, as Creaghorn states, the brain naturally compensates to some degree especially during the more modest maneuvers, but the effect would have its place while one performs some of the sharper moves. It should not feel like riding a boat across the waves, but neither should it be like a train riding a smooth rail. I imagine acrobatic flying to be somewhere in between, FWIW.