We try not to give our hopes up based on a rumor, but it would appear the new Castlevania: Harmony of Despair will feature full campaign co-op. This is great news for Castlevania fans, and will be the next up on the list of XBLA's Summer of Arcade lineup.
"Konami says that players will be able to select "fan favorite" vampire hunters, and while we don't know the full list of playable characters, the art indicates that you'll at least see Soma, Alucard, and Shanoa. Players will use cooperative attacks and teamwork as they explore the massive levels inspired by Dawn of Sorrow, Portrait of Ruin, and Order of Ecclesia."
The Summer of Arcade begins in July, and so far has Lara Croft and the Guardian of Light as well as this Castlevania Xbox Live exclusive.
Source: Gameinformer.com