A fair concept, you know the good things so let me be critical

- The nudge feature may fall out favor in group, I hope you have more arrows in your quiver

- You create a peer pressure eco-system, also look if you can introduce a peer incentivi-zation feature like a badge etc.,

- Will look for a feature where the organizer sets up a pre-event event and a deadline before which money needs to come in

- Also put in a word or two about the transaction security you provide to get some confidence from those early birds

My two cents...