Re: Hope there's a way to disable this
Service Worker background scripts are VERY limited in scope, and can't just quietly sit in the background mining bitcoins- the browser is supposed to kill them dead if they execute too long. Like any browser feature, if you don't like service workers in chrome, disable them in chrome://settings. I am sure Apple will provide a similar option. In general, judicious implementation of PWAs should *decrease* your battery and network consumption over standard browsing (things like the fetch API provides a customisable transparent network cache for the app, and the ability to drop offline in crap network conditions where you would traditionally be re-transmitting corrupt packets).
Surely, service workers are far, FAR less of an attack surface than visiting a site, downloading their freaking binary from an app store with myriad more ways to punch into the kernel, which is the current state of affairs. All that for yet another glorified RSS reader. End users don't even think twice about doing this, and they have moved potentially malicious code through the bulkhead of a browser sandbox, and into a direct user space process.
Unfortunately I agree, the way many sites are adopting service workers is simply to nag you with push notifications, but 90% of the web is shit, and this is just another example of it being shit. Don't like being bugged to install push notifications on a site? Don't visit that site... Long term PWA provide scope for moving beyond Apple's walled garden iTunes store, where Apple skim 30% of *all* sales through your app, and will pull your product from the app store because it mentions there is an Android version.
Sure, like all technology there will be security issues discovered, but just like WebGL when everyone was losing their shit and Microsoft claimed it was far to insecure to implement, fast forward five years and every major browser (even Microsoft's) has an implementation and there hasn't been a string of exploits for WebGL subsystems released every other month like we had with Flash and Java.