The Rebellion being able to merge Devil Arm into the wielder is kinda wierd. We don't know if Dante can do it with another Devil Arm, if the Devil Sword Dante can still do this (since it's originally the Rebellion). I think DSD has been really poorly implemented (along with the Sin Devil trigger). There is no clear explanation of what the DSD can actually do beside summoning sword. And the fact that the Sparda had to be sacrificed to give a clunky new weapon is kinda disappointing.
And the DSD isn't like the Sparda. The DSD can be summoned at will, and we don't even know if someone else can wield it since Dante make it appear and disappear at will. The Sparda was physically always there, and anyone could wield it with enough strengh.
For Vergil, I won't mind giving the Yamato a new form, but he MUSN'T have the same treatment as Dante. The concept art posted by Ronin is really cool (not like the DSD which is meeh), but on how to give Vergil an improved Yamato... Maybe trough introspection and meditation he could actually bind his soul to the Yamato ? It would be a good way to end Vergil redemption arc, to have him at peace with himself and able to grasp the concept of the soul. But somehow, I feel it won't do because of what we saw in DMC 5... Because he haven't change so much after his resurection.
