The proposed solution, to use the ServiceWorker as a trusted cache, is OK when you own the entire origin. Unfortunately, for 3rd parties this is not an option.

The proposed solution, to use the ServiceWorker as a trusted cache, is OK when you own the entire origin. Unfortunately, for 3rd parties this is not an option. There can be only one global ServiceWorker per document/scope. Clobbering the global one by a third party would be unwelcome by page owners, and there's no standard for graceful cooperation here.