Self explanatory. I'm of the opinion that Dawn and Aria of Sorrow are the best games in their respective trilogies, and I'd love to see a return of the soul collection mechanic. Plus, there was something about a huge battle in 1999 that was constantly mentioned in both games. It'd be cool to get more of that back story.
Plus, and I can't be alone in this, I really want the series to return to 2D. Both trilogies on GBA and Ds are awesome and, while Lord of Shadows is decent, it doesn't hold a candle to the exploration and simple but deep combat of the Metroidvania games.