Nowadays I don't even buy a movie upon release unless it's at least a 2-disc set because I know that there's going to be another version down the line.
I'm tempted to get the 3-disc Gladiator director's cut, for example, even though I got the original 2-disc version just because it's supposed to have so much extra material. I would love it if it came with a documentary about all the historical inaccuracies in the movie (I hear there are tons, unlike in Kingdom of Heaven, which is very odd for a Ridley Scott film).
Anyway, I thought that the current Die Hard SE has a ton of stuff? I don't see how they could improve all that much on it.