And it's like he's thinking "it's all going to plan...bwahaha!"
Vergil is giving off some Light Yagami vibes there, I will admit.
But I don't think Vergil will "stab Dante in the back."
I think they will come to a heavy disagreement which leads to their ultimate duel.
After neither can reign supreme over the other in the fight, they give up and part ways for awhile.
That is it until Vergil conceives his plan from Devil May Cry 3.
Now, what will their dispute be over? Maybe about a new character who we all know and already love, Kat.
I doubt she'll live, especially considering the rumors of who she's named after, Saint Catherine.
I believe Kat's death will be caused ultimately by the hands of the twins.
Either because they couldn't save her, had a blatant disregard for her life, or if one of the brothers, Vergil of course, had killed her. Why? Well for several possible reasons, even just getting in the way.
The point being, her death will serve as Dante's moral compass.
As opposed to a duel with Mundus, Lilith, her child, or even Vergil, the true climax will be her death because it will be in my vision the turning point that changes all the characters, particularly Dante. The rest is either rising or falling action.