We've got the same problem. Won a Startup Weekend and have a big team (6). We've debated a number of options here but everyone seems very committed so far, so right now we're working away on it and giving it a few months of breathing room to see if people naturally fall off or lose interest. I'd suspect after a little time you'll start to see who's really dedicated to the project and who isn't. Otherwise, it'll be time for an awkward team conversation about how to proceed.

I would argue that some people whose roles might seem more relevant post-launch may actually be really helpful during the development stage too. If you're looking to customer validate throughout the development process then a talented non-technical person could be super helpful in pounding the pavement, getting feedback, setting up meetings and building relationships for you. So I think it's more about having a small team of the RIGHT people rather than a small team based solely on their presumed job titles.