"The times, they are a changin'... "
The WebRTC experiments module https://moodle.org/plugins/view.php?plugin=mod_webrtcexperiments looks like a great start and has a lot of potential. I recommend trying it out and thinking about how you could use it in formal and informal learning scenarios. Because it's so easy to initiate a conference and invite classmates, I think think it's more powerful than traditional media server based conferencing.
And yes, Web RTC runs in all browsers on all platforms except for IE (Microsoft have announced that they will support it but have been dragging their feet) and there may be some limitations on some mobile devices. Web RTC is a peer to peer protocol so it doesn't require a media server but, like Etherpad, does require a server-side client to coordinate who's connecting to who.
Check out a quick demo of WebRTC here: http://blog.matbury.com/2014/09/02/instant-simple-video-conferencing-free/
And Mozilla has an open implementation of Etherpad to use here: https://etherpad.mozilla.org/
Web RTC is very new and most applications of the protocol are in experimental stages. If there isn't a shared whiteboard already available, I'm sure there will be one soon.
So... stable, reliable, and affordable multimedia, multi-way collaborative web conferencing is just around the corner and some of it is already usable.