Show an indication in the voice channel that a user is currently live.
Show an indication in the voice channel when a user is currently streaming in that specific and show which user is live.
Interestingly enough, the API already documents the "Game Type" called "Streaming" which would allow for this kind of feature, however, it seems to not be used.
OP Please add Tim's comment to your suggestion!
It would also be awesome to have a confirmation before they join they have to acknowledge that they'll be broadcasted like Hangouts On air did: https://imgur.com/a/6k0Ms