How do you plan to accommodate NoScript users?
By knowing how the sausage is made, I'm also aware that the line marking the aforementioned certain point is often drawn too early, at informational (i.e. document) stuff where HTML and CSS are fully capable on their own.
In fact, JS is extremely useful in the browser. It adds to the richness and interactivity of webpages. We must collectively appreciate this, and stop denying this! Even HN is a better experience with JS.
Some sites do give JS a bad name, and poorly used JS is something I hate too, but JS as a concept is something that I wholeheartedly support. Thankfully, the web is mostly opt-in - if you don't like the way a site employs technology, just don't visit it. Simple.
Slow internet connections are a reason to think about the experience when loading JS is slow and/or failed. It's not just 'poor people' who have slow internet - 'rich people' on inflight wifi or on the internet on the train can result in things not loading.
Ok, we do assume that you have visited our webpage at least once in an area of strong signal, however, once you've done that, all the JS is cached and all we transmit back and forth are lightweight, gzipped json payloads, often less than a kilobyte.
I use my own PWA regularly, and found it actually quite usable in-flight.
If you do not server-side render, it does not matter whether you put your CSS into JavaScript or not—your JavaScript app is not going to render anything anyway.
NoScript users are like the customer that demands the most but pays least. After some rants of such customer, they're ignored.
It's rather easy too if you're using a (great) library like styled components - this functionality is built in and just works with a couple of extra lines of code.
The deeper question here is will the app work at all without JS. That's quite hard to achieve (every client side interaction must have a server rendered equivalent accessible via a url or url params, essentially) but the CSS part is easy.