Yes and no.
I did pay for app.net when it started, so I know that I really would pay for it. App.net had a theory that if you made an elite social network, interesting people would pay to be on it, and then everyone else would follow.
In practice it seems these don't really work, when there are free alternatives.
On the other hand, the public social networks are becoming too abusive for many subgroups so maybe that would be a place to start.