if we’re talking about the broadcaster getting information as to what the viewers are doing in the extension, this would have to be done on a per-extension basis by the extension’s developer.
Since Extensions use WebSockets, the Extension could simply report back to the Extension’s back-end server, and then report the aggregated information back to a front-end panel that the broadcaster uses.
Not specifically Extension related, but our custom channel bot has a giveaway feature that, via SocketIO and TMI.js, is able to communicate with the chat room (TMIjs), a Dashboard client i wrote (SocketIO) and our on-stream widgets (also SocketIO). We can see lists of entries, have controls for the giveaway itself, and all giveaway information/events are piped to the widgets in OBS to show live stats while the giveaway is running.