If you're not looking to differentiate via software/killer features, then the platform is less important than your execution/presentation and most importantly, marketing. I assume you feel there's some group of people not being properly connected, so I'll just assume you need to give them the place to congregate. Best then to begin on something that's already reasonably stable and adjust it as you go.

Social networking is still a viable niche in some cases, but it'll be very hard to monetize (if that's what you're after).