Harmy said:

That is not what the BD looks like. But if there were scenes looking like that, I would simply add some grain.

While this would make the picture look more natural at first glance, it doesn't bring back the image detail that was lost in the DNR process. I know that there are some cases in the trilogy where you added digital grain but I don't really see a real benefit in this. It's just adding something artificial to the image instead of bringing back the original grain and the image details that were removed with it.