A lot of those problems are a lot easier to solve with a smaller audience.
My point is, you haven't solved Twitch's problems at Twitch's scale.
All a team can really do is setup an architecture that can theoretically scale, and then adjust as you reach higher and higher levels.
FWIW, our site is actually a pivot after a product that reached a higher unique per day than twitch currently has (99th globally vs 63rd globally according to alexa.com). And I can say from experience that scaling a real-time experience is MUCH harder than a more traditional web app experience. But the techniques are much the same, reach the scale, see what breaks, fix.