Interesting, but flawed theory. My mother has a Jewish maiden name. They came from Czechoslovakia, but several generations earlier, her great-great-great (whatever) grandfather worked - and lived - on a farm owned by a Jewish family. He took their name because he had a permanent home on their land. So, although he was ethnically Czech, and religiously Byzantine Catholic, my mother's family had a Jewish surname.
This could be the case with the pope's mother's family.
That said, it would only increase the stature of John Paul to find out he had Jewish blood.
My family has a Jewish sounding name but we are Catholics. Have a friend who is Jewish but one would think Irish/German by the name.
Whatever his background, Pope John Paul II was well-loved by people of differing relgions and backgrounds. All humanity was blessed by having him in our lifetime.