ITB is not. has not, and never will be a replacement for the Demo campaign. Imagine as if the Demo was the FS2 main campaign, and Den5 made a fan campaign, which happened to cross paths with the main story, so he borrowed a few missions from it and then added in his own story ships to make it fit.
BTW, I tried to fly the Demo campaign recently to see if there were any further story events I could borrow, as I hadn't played it in a LONG while. Unfortunately, I wasn't able to get past the first mission, because some key event didn't fire. When I EVENTUALLY get ITB ready for re-release, I may have to take a closer look at EMW Demo and give it a face-lift.