I think the primary challenge is convincing users that it's secure. Snapchat has a relatively poor reputation in security (whether that's deserved or not), and everyone I know just uses Venmo. Venmo has Facebook integration, so if you're Facebook friends, it's really easy to send money.
It seems like integrating into a platform that's supposed to be ethereal is a weird fit, but who knows -- maybe it'll catch on.
It seems like integrating into a platform that's supposed to be ethereal is a weird fit, but who knows -- maybe it'll catch on.