One way to prevent a CDN from seeing every request for a shared resource could be a new attribute that allows serving the resource locally if the resource is not in the shared cache.

For example, <script src="/jquery-3.4.1.min.js" try-shared="https://code.jquery.com/jquery-3.4.1.min.js" try-shared="another-src">

@src can be locally hosted. If it's not in cache, the browser can try each @try-shared attr (without loading the resource from CDN). If no match, the browser downloads @src from your own domain.

Of course, this doesn't solve the Shared Cache issue raised by the article. Suppose the only way to solve that would require adding resources to the shared cache explicitly. The most effective way (I assume) would be a header provided by the CDN of a shared resource, eg, X-Shared-Cache: true, that a browser would recognize... Then @src/@try-shared could still get the benefits of the shared cache and developers don't have to worry about it.