JES,
At first, I was put off a little by your reply. After more thought, I can understand how you believe that eventually, the thing will be used for pure evil! At the very least, its use will have some unintended consequences, just as the stimpmeter did. While at first I figured trying to get the approach areas as firm as possible would be a good thing, the next logical step would be to strive for perfect consistency.
Clubs may strive for the same reading in front of all greens. Whether that makes any sense I will leave to others, but with more variable slopes in front of a green I believe it would be harder to attain than on greens. And if that leads to flattening of approaches to a "standard" slope so that golfers can better predict how their approach will react, then I think the thumper will inadvertantly take golf in a wrong direction.
Even if not flattening, there is already a micro trend to extending the sand out the approach for a more consistent run in turf condition, and in many cases extending the herringbone out the frontal approach, too. At the very least, this will increase construction cost and comlexity yet again, or at least has the potential to do so.