webinars addon
oooh baby- connected with rsvp and tickets or simply done an an open event

Online webinars are huge- you would have an event and the ability to add a streaming video (live) and an online group chat.
people who buy webinars addon may also be interested in buying tickets or rsvp, countdown timern reminders and also the speakers addon for large online events/conferences

video playback would be on the event itself- perhaps with a customized single event page where the chat option would be in the side bar (or put the chat somewhere else)
you would have to buy tickets or rsvp to view the video and event managers could manage the online chat and kick people if needed- you could have multiple admins to the event who can also respond as admins in the chat
more ideas on webinars if you want them