So, the idea is, for twitch viewers that sync their Bnet accounts - allow/enable them to participate in the in-game + party chat of the streamer they’re watching… Obviously “announce”/promote this feature heavily / constantly, and allow for it to be opt-ed out of.
Might also consider working out a deal with Twitch to create: Official SC2 24/7 live ladder stream(s), have it showing multiple games PiP style/squad stream with itself, always streaming ladder on a 2-5min delay (better than hoping / searching for replay packs).
With the plug-in have it so viewers can “cast/view” the steam/ladder games themselves, like with access to some of game’s observer features through the browser/plug-in.
Could throw vetted ESL casters a bone too, giving them constant supply of work, just casting random ladder games when ever they want. 