Something that would come in mind for a musical hangout
connecting 10 Singers from 7 continents for one song
Livestream it to other social networks,

When the last Hangout bug happen over 80 people could go live in one hangout so the technical limitation are just partial. Feed it from G+ to FB embed into Pinterest and conducting via twitter there should be no borders between the platforms at least not for the user.

Lets see what happen next much more to imagine.
Thanks to +Anni Paananen to point me on these gorgeous project

VideoInfo: The 2011 Virtual Choir video features 1752 singers in 58 countries, individually recorded and uploaded to YouTube between September 2010 and January 2011.