I foresee a possible 50GB BD disc for each DE 3.0 film with all the audio tracks and commentaries (1 disc per film), paired with a complementary 50GB BD disc for all the special features for each film (1 disc per film), resulting in 6 discs. At least, theoretically. I haven’t done all the math involving current items and size yet, but this is a start.
yes, once 3.0 is released (far off), someone would need to start a new set from scratch, as the filesize of the 1080p release will throw everything off. I agree with the first disk just the main feature approach at that point.