In that there aren’t any other Pope Francises, it’s incorrect to refer to him as Pope Francis I. It would be like referring to John Smith as John Smith, Sr., even though he didn’t have a son named John Smith, Jr.
No one refers to Pope St. Agatho (678 - 681) as Pope Agatho I. There were no others, and thus, Pope Agatho is more than sufficient to identify him.
Thus, Cardinal Bergoglio should be addressed simply as Pope Francis.
But hey he is the first with new title so that is why I call him Francis I.