considering how fast people are downloading STO beta client.. It sure sounds like a success from the start.
on FilePlanet there is 160.000 downloads at this moment. And there are plenty of sites around serving the client.
With the minimum of 50$ (or 50 EUR in Europe) per entrance and if you decide to buy the subscription (which would be how much? 10-15$ per month?) that is ~11 mil $ per year if they have 50k subscribers. And I believe they will have more than that.