I was very concerned about that, even though the capsule had a parachute...crash landing in the desert would not be good.
That being said though, I would think it might be possible to use a much larger balloon...but then again...you know, that one was 700 feet tall and it seemed like the real challenge was getting it off with no wind at that height. So, a balloon of say, 900 feet, would be much more difficult. No, I think that Felix's record will never be broken. Why even try? The next challenge will be freefalling from...outer space...without burning up. (Think Iron Man)