I had heard that the plan was to open the IR several years ago from many credible sources. I had heard that it wash pushed back when Chef Major came in so he could have time to develop the menu. Since this was a few years ago at this point, it's safe to say that the plans were either shelved or weren't very serious in the first place. I think their their concentration on the culinary experience of events has shifted their concentration.
Personally I'd love to see it opened. Even if it weren't on the meal plan. It likely wouldn't be. It would be cool to go up there for a nice meal for special occasions. Especially if you could schedule a reservation on the app or something. The original intent was to have it open all year, although I don't see that happening.
The IR is used quite often for special events. In addition to that it is used for employee training and meeting space. Although it is not open to the public very often, it's still very much a used space.