There is one easier classification, a series of herd paths saparated by the luck of the draw which, as others have pointed out, may vary considerably on the basis of the season, or a mere matter of 30 yards.
It makes interesting discussion but I would find a bushwhack classification system useless.
First, if I'm looking for a description of a bushwhack a classification system doesn't tell me much other than one person's experience on one of, theoretically, an infinite number of routes. I prefer a much more qualitative description of the trip.
Second, unlike paddling or rock climbing where the classification is based upon relatively defined routes and the classification system is helpful in keeping participants within their limits, bushwhacking requires two things, navigation skills and the will to put up with it or perhaps the perspective to enjoy it. Without those requirements, don't attempt it because a "1" can turn into a "5" at slightest the wrong turn.
Finally, can't we leave the rat race out of at least one aspect of hiking? Do it for shear pleasure, not for bravado. Keep score by your scratches, achievements and disappointments, and willingness to go back.