Since its a two piece barrel, it would be a lot more difficult to make a 3 inch version than if it had a one piece barrel. The barrel shroud is not something that could just be cut off, it would need to be a new forging. Or casting; I am not sure how the shroud is fabricated.
For some reason, S&W has determined that a Centennial, and only a Centennial, without an IL, is safe!

Best,
Rick