Unfortunately, you likely can't ask them that intent. I worked with Knowclick, which is a company that combines surveys with analytics of user behavior to try to derive intent. And, it's interesting that people often say and do quite different things. But for intent with a social platform, first you have to get them hooked on the value. You can ask them basic questions about value or features they would like to see. Or, employ an NPS survey mentality. Ask them how likely they are to refer the platform to others on a ranking from 0-10. In order to build the platform, you need scores of 8-10 that indicates that you have evangelists who enjoy or see so much value they are eager to tell others about. If you haven't read Platform Revolution, I'd it for a primer on challenges and strategies to building out both audiences -- including one that pays and one that doesn't-- in a timely manner.