One of the increasingly popular uses of JS is to save bandwidth. Using JS, you can ask the browser if the user is on a metered connection or an unlimited one, what their estimated bandwidth capacity is, what their real resolution is, and load appropriate assets (or conditionally load content). With JS disabled, a user on a pay-per-kilobyte 360x640 cellphone is going to get assets deemed acceptable on the manager's 1440p desktop. There are already quite a few websites where disabling JS more than doubles your bandwidth usage -- and sites that are only even usable in third world countries because of JS like this -- and that's going to increase as screen and media quality grow.
Not to mention the huge accessibility benefits that can come from changing the way a site behaves (not just visually but in terms of things like tab and focus behaviour or separating components out) for disabled users. Doing that reliably and effectively for all content on all devices is much easier if you can identify the needs before downloading the content which means JS-loaded content and so it can come down to deciding whether to annoy NoScript users or disabled users.
That doubtless provides some reasonable bandwidth savings on certain media sites, but I'm pretty sure the whitelisting approach is going to come out far, far ahead in general, as most ads don't load and some Javascript assets are themselves megabytes in size.
Also, IME, disabled users hate javascript. But my experience is limited to a few vision impaired folks.
Why, if your goal is to save bandwidth, would you have the system default to loading the biggest assets when you can't ascertain these things, instead of loading the smallest ones?
That said, given my experience of running the web with NoScript, I'd be surprised if those sites that double the usage when they can't detect these things come anywhere close to eating up all the bandwidth I'm saving by not loading auto-playing video ads.
Not to mention the huge accessibility benefits that can come from changing the way a site behaves (not just visually but in terms of things like tab and focus behaviour or separating components out) for disabled users. Doing that reliably and effectively for all content on all devices is much easier if you can identify the needs before downloading the content which means JS-loaded content and so it can come down to deciding whether to annoy NoScript users or disabled users.