I am curious as to what people would answer to your question. My ideas also revolve around a business model that needs a social network. But i plan on grabbing a niche market which this social network would revolve around and thats where hopefully the money would come in.
I think if you want someone to pay for subscriptions there has to be a need for someone to pay them. Probably something that revolves around their everyday life or something that requires constant attention. Unless you have something that could get people addicted and have this need to come back and use it. lol!
You might consider private label options - i.e., what are the functions for which companies or organizations might pay to have within their network?
I think it depends on your network. start by finding out who's interested in reaching your network or vice-versa.