Prof. Sofer has been talking and warning about the Demographic time bomb of Arab citizens in Israel for decades. Of course from the campus of Haifa university which is full with radical Arab students he knows better than most people what he is talking about.
But, as far as I know sofer believes in the Lieberman approach of detaching Arab populated areas from Israel. I think if it was more acceptable to speak more openly he would actually support JTF's suggestion rather than Lieberman's.