Oh damn oh damn, I was just about to reply to this comment and say
"if you follow through with this great idea, I'd suggest using synchtube. It takes a source video, like livestream.tv or youtube and is sort of like a event hall or lobby where it's synched for everyone and there's a chat on the side. Also, no ads."
but then I visited the synchtube website and realized it was down!
Now I'm having a minor panic attack because I've made so many friends there, it's honestly been a huge impact on my life.