The requirement to disable SIP in order to make use of WebKit build archives is not ideal. A code-signed nightly Safari would be very helpful for some customers.
In support of this request... We at Salesforce are struggling to test our membrane implementation with the new ShadowRealm API. Any easing would be appreciated!
Since this is not a WebKit issue, we cannot track it in Bugzilla. This is being tracked internally at Apple. For some uses, MiniBrowser can be a workaround.