Johnny said that too years ago: that he expected Kyrie to die or being a villain and Nero becoming a darker protagonist. Johnny was not too happy with DMC4 ending.I remember on one of the last year's con Johny said that it could be nice to show dark side of Nero. I guess thet could be great opportunity to do this.
But there could be trouble to show it in a unique style. If this fight will become a re-playing Dante-Vergil fight and relationship... that will be kinda boring xD
Artbook goes on how Nero would become a power seeker if Kyrie dies and how Nero is very similar to Vergil. It seems they threw away Vergil just to do a Vergil 2.0.