To offer a little feedback: Focusing on an immediate deliverable that solves a finite problem was good, but I think the proposal was structured in such a way that it asked for too much commitment too fast.

A "hackathon" has a short time horizon. At the end of the hackathon you'd have some idea as to whether or not you'd want to continue, regardless of whether the goals of the hackathon had been achieved. Give people a chance to try out contributing in small amounts, and to evaluate whether they want to continue contributing.