I think the fundamental problem here is that ToS need to be written to be as generic as possible. If Snapchat wrote a ToS that legally bound them to the exact w

I think the fundamental problem here is that ToS need to be written to be as generic as possible. If Snapchat wrote a ToS that legally bound them to the exact way that their app works today, they would have to get a lawyer involved with literally every feature change they make (or feature experiment they run) in the future. The very reason most people use snapchat in the first place is that they expect a very limited featureset with tight controls. It rightly should be a cause for concern that they're making way for expanding the scope of the service.