We'll have a free plan, but in general, no it's not free. Neither is DNS though (it's free for the end user of course, but not the developer, just like Firebase).
The title of this post should be "meet a more client heavy version of WebRTC", because that's what it is.
See: http://www.html5rocks.com/en/tutorials/webrtc/basics/
"In the real world, WebRTC needs servers..."