When it comes to live streaming, the viewer contributions are pretty light. In Periscope, you can drop a comment of leave a floating heart icon, but there isn’t a deep way to contribute to a stream. Today, Twitter is rolling out a change to Periscope that hands broadcast viewers the microphone, allowing a video stream to bring audio-only call-ins from the audience.
To answer your first question, yes, Periscope is still around. To answer your second question, the streamer has to hand the microphone over to individual users, it’s not a free-for-all audio call, that would be unimaginably awful.
The feature seems to be a way to bring out deeper interactions with a streamer’s audience. The commenting systems on a lot of these live platforms turn into an indecipherable wall of text for most users even if the streamer is able to keep up with them, therefore the dialogue really ends up moving in whatever direction the broadcaster deems.