Some hopefully constructive thoughts: There's nothing about the landing page that makes me want to sign up. Could you show me an example of how it works, what it looks like?
Ideally I think you'd want to seed it with pre-existing conversations, so that new users don't feel like they're signing up for one more thing that doesn't have any obvious value.
Chicken-egg problem– Quora, Reddit, and I'm sure HN itself all started with a small group of people who were having interesting conversations.