That sounds like a really fun and clever concept! It takes the thrill of zip lining and adds a precision skill challenge on top. The idea of dropping a weighted bag and scoring based on accuracy gives it a competitive edge and replay value, especially if you mix in different target sizes, distances, or wind conditions.
You could even add variations like moving targets, bonus points for trick shots, or timed rounds to make it more dynamic. It has the feel of a simple-to-learn but hard-to-master game, which is perfect for players who enjoy both skill and a bit of strategy.