Nero, Credo, Agnus and Arkham.
Nero because the guy has a lot of potential, but he was messed around in DMC4. I want a backstory for him and some character development that does him justice.
Credo because he is awesome and I think more can be done with his character.
Agnus because that guy is creepy and I think more could be made of that if he was DmC style. For example, more detail about his experiments with humans and demons.
Arkham because I like his character. He's sinister, and was smart enough to maniuplate both Dante and Vergil to get his own way. Also, I want to see how a DmC styled Jester would look and sound.