If they want to make a "sequel", telling the 1999 fight would be the best route. A game in the future of Aria of sorrow would work as well. In the last scenario, not sure if Dracula would be the villain as he was finally defeated but probably an iconic vampire like they did with Barthory.
I wouldn't be mad if characters like Sonia, Nathan Carrie were added in canon using their concept but maybe in the modern times to make sense in the timeline, or something like that.