I don't how the fight would go, but a second phase where Dracula absorbs Simon's curse as a last-ditch powerup would be pretty cool.
Believe it or not, I wanted something of the sort for the end of Curse of Darkness.
To be honest, the end of that game disappointed me. I DO love the bit how, pre-CoD, it took 100 years for Dracula to be resurrected in full. I'd keep that had I been in charge of the story. My ending would be with Isaac being used as the vessel for Dracula (same as CoD, but his appearance would be Isaac with the energy silhouette of Dracula's form), but when Hector defeats him, Dracula's spirit is sent back into the abyss (no second form) and with the Curse lingering, Hector uses his Devil Forging abilities to transform the curse, not into something harmless like in the game (because I'd say that devil forgemasters could only forge physical monstrosities from evil energy), but into a singular form of evil, a giant beast made up of multiple demons, heads, arms and such. I'm visualizing something akin to a CV-take on Neo-Exdeath (Final Fantasy V) and less Menace from DoS.
Now getting back to CV2, had I designed the game, Dracula's Ghost's first form would look more like Dracula and less like Death. After the first form's defeat, Dracula's Ghost would pull all his remaining power and transform into something similar to HoD but more modeled after the final form of the final boss of Ninja Gaiden 2 (NES). Simon will be warped to a dimension of darkness (black background) and Dracula will appear as a giant demon with is own demonic face attached to a giant, rotted skeletal body, chest ribs open, giant heart beating (weak point), and massive floating hands with sharp claws, a giant eyeball that appears in his mouth that shoots out beams and sharp bones shooting out from his spine. He appears in three places, the right of the screen, the left of the screen, and from above. Right or left, he'll function the same, attacking then exposing his heart for damage. When he appears above (like his head is peaking down from above the screen), he'll drop deadly wads of blood on Simon.