AMP is not supposed to necessarily replace existing pages, but can rather be cre...

AMP is not supposed to necessarily replace existing pages, but can rather be created by publishers as lightweight/performant alternatives for mobile visitors arriving via Google Search. Hence why you can declare

    <link rel="amphtml" href="/yourampversionofpage" />

in the normal page.

Those with JavaScript switched off probably won't be suggested the AMP pages in Google Mobile SERP.

So you could serve the JS-optional pages to all clients, progressively enhance for JavaScript users and offer AMP pages to mobile JavaScript users.