Well, re-skinned Dante would suck, but even DMC3:SE didn't so that, it was a Vergil model that behaved its own way, and they just added 2 new opening cutscenes just for him and one secret movie at the end. Everything in-between was playing as this new Vergil through old missions (I do like that they gave Yamato a 'darkness' element to do cool kinds of damage to Beowulf and Fallen) So if it's exactly like DMC3:SE, then we'll get 2 explanatory opening cutscenes, a play through of all the same missions (with a few tiny tweaks) and a secret movie at the end.
Question: What about Nero's missions could Dante probably not operate through, and what about any of Dante's missions could Nero not get through? I'm assuming most of the answers will be "Nero got from point A to point B with DB. Also the Slicers." I honestly imagine Vergil's Darkslayer techniques could be used in place of Devil Bringer. Instead of grab-and-swoosh, he just poofs in the intended direction.
I will be satisfied if everything gets a graphical update (audio too) there is noticeable rebalancing and added sharpness to movement and such, that Vergil is playable and somewhat fresh gameplay (at least for him) and this opportunity is used to add scenes clarifying Nero's origins and/or relation to Vergil.
And additional costumes.