Hmm... Metastream looks like it would work, but it only handles syncing our viewing, and everyone has to have a paid account through whatever service the video is coming from (Netflix or Hulu or whatever if it's a paid site).
One of the Youtubers I watch (Markiplier) uses XSplit and he hasn't had any problems with it, though I don't know if you can stream its output to anyplace you want
We could play with a few streaming sites, I know derpy.tv did a 3-day marathon leading up to the series finale of MLP this past Saturday, streaming stuff from harddrives and for the finale, switched to live TV (at one point, they had 850+ viewers)
Yeah, that's kind of the issue, too... I don't think any of us would cry "copyright violation" if we showed a marathon of Carmen or Ghost In The Shell where only logged in users could see, just like Youtube has an issue if I post a video and there's a song in the background
True... for those who have any games (all I have since the last botched reinstall is Minecraft... lost GTA5, Arkham Asylum and City, the XCom games), but it's kind of fun to watch others play and still be able to chime in