Even though the Cast SDK has been open to the public for about a month now, there has been no implementation from Twitch.
An independent developer has created a app for Android called TwitchCast. This very simple app now allows users to cast Twitch to their TV’s. Over the past few days I have been using this app with no flaws, everything is smooth and the same quality when using the Source option. If you have bad internet be sure to check out the other lower options. Unfortunately, they only apply to users who are Twitch partners. Recently Twitch did announce the availability of multiple quality streams to non-partner users during off-peak hours. Bottom line, Unless you know they are a popular streamer, don’t attempt to use any other options other than source.
If you are looking for a web based version to cast Twitch, look no further. TwitchCast Web