If this has a section where Dante has defeated Vergil and sent him to the demon realm, perhaps the demon realm will antagonize Vergil by creating a Dante doppleganger.
Yeah! And make him battle his own shortcomings of being a more compassionate human!
I'd say if Vergil's Downfall had at least one exclusive boss, it would be fantastic. It would be really cool to see how the game's AI would make Dante fight, too, but I'd settle for something over-the-top crazy just to accommodate for Vergil's moveset.
That was another misstep with DMC3 - Vergil just being a character swap made a lot of stuff unnecessarily difficult because of his different playstyle. By making a scenario built around Vergl's gameplay, the possibilities are just...ugh...fhdsjlfhadfhjabvalwuv