I wanted to add one point in support of your idea, DonsAdvisor:
In the deleted scene, Neri says of Fabrizzio, "He entered this country in 1956, sponsored by the Barzini Family." Now, as we know, Barzini was killed in the Great Five Families Massacre of 1955, and the assumption was that all serious opposition to Michael was eliminated. Yet there had to be someone left in Barzini's former family who had enough clout, and presumably, hatred for Michael, to remember Fabrizzio and bring him to America, and set him up in a pizza parlor. Was Fabrizzio supposed to be a kind of "Manchurian Candidate" or "long trigger," put in place to make another move on Michael in the future?