I've resorted to checking navigator.userActivation, which was also added in 16.4, as a workaround to display the "Add to Home Page" message.

A typical feature based detection uses "PushManager" in window and showNotification" in ServiceWorkerRegistration.prototype to check whether a browser supports notifications and eventually display the "You need to add the site to the Home to get notifications". With the Safari experimental settings (Push API and Notifications) disabled though these two checks fail and there's no way to distinguish between this case and a browser which simply does not support this technology. Is there a workaround or another requirement? Also, even if I add the site to the Home Page, even with a Manifest (which I'm sure is loaded as the background color changes), both checks above still fail. Is there another requirement to make feature based detection work, maybe something in the Manifest? Thanks!