How is installing a native application a viable alternative to javascript? Presumably, if you're blocking the latter is because you don't want to run untrusted code on your device.
Twitch does have an IRC gateway, so it's possible to use your own application for chat.
As another poster commented, the video aspect can be fulfilled with a number of different methods, and I don't see any technical reason a standard couldn't be followed to allow for arbitrary clients to handle that interaction as well.
As another poster commented, the video aspect can be fulfilled with a number of different methods, and I don't see any technical reason a standard couldn't be followed to allow for arbitrary clients to handle that interaction as well.