What are the connotations of "Al P?nei Kol Echav Nafal"?
Rashi #1, Rashbam and Targum Onkelos: It means that "he dwelt (encamped) in front of all his brothers". 1
Rashi #2: Here it writes that Yishmael fell, whereas earlier (16:12) it writes that he dwelt? As long as Avraham lived, he dwelt (safely); once Avraham died, he fell/
Targum Yonasan: It means that he settled in the land of his inheritance in front of all his brothers." 2
Ba'al ha'Turim: It juxtaposes the fall of Yishmael to the generations of Yitzchak - to hint that when Yishmael falls at the end of days, Mashi'ach the son of David, who descends from Yitzchak, will flourish. May it happen soon in our days!
Ha'amek Davar: Initially, Yishmael was not a strong enough nation to conquer and expel others, just they fell upon (raided) them. Later, they increased, and dwelled in serenity and other nations feared them.