Why are Google Hangouts a viable alternative for people who care about privacy? (Ostensibly the point of this article.)

I agree. Distributed and P2P with encryption is the only way to guarantee privacy.

first, make yourself familiar with WebRTC. it will require server side signaling. demo by google: http://www.webrtc.org/running-the-demos#TOC-Demos sending srtp session keys over that signaling server sounds interesting