I would do something that many might disagree with. I think to show people's true nature, they would have be unaware of being filmed. I think the problems with shows like Big Brother is that the candidates knew that they were going on TV, they knew it was a game an the 'game show' selected people who they knew wouldn't get on to make sure they had an entertaining programme.
I would do something like 'Shipwrecked for real' and make people think that they are all going to a desert island for a date programme, and then engineer a storm where the camera crew get lost, or maybe their equipment does, and then they have to work out how to get to shore and how to do everything else.
This would have to be done in a massive studio, much the same as Truman's world in the Truman show so that everything could be controlled, including the climate, how calm the sea is.
This may seem like a very evil plot, however, it has been proven that people who are lacking in ambition often need something to happen in their lives to force them to take responsibility and take action to move on from a rut they are stuck in, and this could be a great social experiment with people in that frame of mind, so that once they have survived and they realise how much they really are capable of, they will realise the sky is the limit.
Legally, this would be torn to shreds, but I would still enjoy making it to explore the psychology of human's behavior in groups in emergency situations. Who takes the position of leader and why? Does everyone trust them, is there a coop, would they have really survived that situation had it been real? (obviously emergency services would have to be on standby). I think people would be hooked and we would learn a lot from some poor unsuspecting volunteers.