With the recent shuttering of AIM, I'm reminded of the old client's Direct IM feature which would allow you to transfer arbitrarily large files through the chat session. That tool could not have been simpler to the user, as they just had to click "Direct IM" and could then drag and drop files into the chat. However, that system still relied on the cloud service (AIM) being a broker of connecting a handle to an IP address, and that there was little guarantee of the identity of the person on the other end of the IM.