It's amazing how many sites won't even load nor give you a warning when you just opt out of JS (e.g. by using an addon like NoScript). Even very big ones, like twitch.
Don't rely upon it to exist.
Serve up well marked content, CSS that might format it nicely, and JavaScript that allows some types of per-validation to happen client side but only as a means of making a page nicer. The server side should STILL perform all data validation, normalization, and verification (assume someone will craft their own form submission).
Twitch could be done with a native app... the phone versions SHOULD be done with such if they aren't.
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 for video streaming, that's not hard at all, especially now that there's a <video> tag.