I think no matter who you are, going from a situation where you know no or few people who live close to you, to one where you suddenly know and have access to people who are within walking distance would make a huge difference on your life. Will that solve all of a depressed person's problems? I don't know, but I think it could go a long way towards helping them. Access, in my opinion, is the main issue here. That's what I'm working on.
Sure, some could probably help, but I imagine they'll either be palliatives (like 7 Cups of Tea) or enablers for human actions (like Skype). I normally assume that "startups will solve it all!" is more of an exaggeration than an actual opinion, but this thread has me doubting myself.