When you think about it the supposed original story for 4 about dante losing more and more of his humanity ties in nicely and would be a pretty good connection between majin form and sin DT. In 2 Majin DT could be seen as Dantes human half failing and his demon overcoming him for the sake of survival, introducing a disonence between his human and demonic blood. Then 4 happens with dante losing his humanity in his perfect DT form. Im not too sure of all the details of what that entailed only that it aparently ate at his humanity. I think if we got that it would make for a better pay off in 5 when he finally unites both halves so he can use the tremendous power with him losing himself. Even giving more reason for nero to need to as "dante, is that you?" Hes making sure dante hasnt lost himself again. V and urizen could even use this same logic explaining why reformed vergil is more moral. His demon blood is no longer driving him