I don’t know how many people are claustrophobic, but for me this would be a non-starter.

Edit: apparently 12.5% of the population has claustrophobia. If 5% of flyers choose a different airline due to simulated windows that would wipe out any cost benefit from fuel savings.

I don't think it is that simple. If a route has mixed offerings and the cheaper option is the windowless plane, it's likely to be full and they'll save on fuel costs for the full flight and can charge extra for a normal flight off hours and come out way ahead.