I think that's an interesting idea. The first thing that jumps out at me is that it better be very simple to use, and there should be a way to integrate it well with the church website, regardless of what system they use to run their website. But, I'm sure you've thought of that already. I don't think this would work out well for my church since we're pretty small at this point (about a hundred attendees most weeks) and not particularly tech-literate, but I'll keep an eye on this.