I think this is great, but the timing is strange. Many Node developers from around the country (world?) will be in the Bay Area from June 27-30 for NodeConf, a couple hours outside of SF. It seems like it would be better to put on a Node-related event in SF right before or after NodeConf.
Great to see the Meteor team engaging with the developer community and organizing a hackathon. A great reference for anyone organizing one of these for the first time is the Hack Day Manifesto: