I haven't read through all 67 replies (!), so maybe this was suggested, but in the 2-minute cardio segments, how about 1 1/2 minutes of aerobic intensity moves, followed by a 30second plyo/anaerobic blast? The aerobic segment could be a lower intensity version of the blast.
I love the idea of putting the core moves at the end. I usually do "Boot Camp" by playing the "all but core" premix followed by "core only" premix.
For the 30 minutes extra, what about a 15-minute long stretch (athletic, not yoga) and 15-minutes of upper body resistance work, perhaps usiing a medicine ball (from the above description, it doesn't look like upper body resistance is planned for this workout, or did I miss something). This upper body work could be combined with segments of the original workout in various ways: new circuits, a resistance-only workout, cardio and upper body, etc.