That would be pretty awesome.
But what I am thinking is that Vergil is the one who is going to be having an Angel Trigger of sorts. You can see how angel moves and stuff have this blue color about them while demonic stuff are all red. This might mean Dante is more demonic or he is becoming a demon while Vergil is on the other side, he becomes more angelic.
In past games, the reason why one was blue and the other red was because Sparda had this purple demonic powers. So both blue and red color powers of the brothers were demonic, indicating like a division of Sparda's powers between them. But now that the brothers have a demon father and an angel mother means that these two powers can be divided into those. So essentially, Vergil is more like Eva while Dante is more like Sparda... sort of speak.
No offence. Yours theory is good too , Thinked similiary about that.