I like the "adopt as tab" button idea a lot and generally agree but I also see the associated risks with other suggestions.
For example, write only access to history will also mean SEO-consultant-type people paying app developers to write certain websites to the users history. When Safari does suggestions on the address bar, browsing history is a major source.
The only caller of said API would be the SFSafariViewController itself, the same way the Share Panel can see your Contacts despite you not having given the app that opened the Share Panel Contacts "access". This way, only organic page navigations get recorded (or at minimum is equally susceptible to any history pollution as a normal web page that you encounter). The idea was not to have SFSafariAddURLToHistory(), apologies if that's the way it came off.
For example, write only access to history will also mean SEO-consultant-type people paying app developers to write certain websites to the users history. When Safari does suggestions on the address bar, browsing history is a major source.