With only a few days till the 10th Movie DVD is released in Japan, the Official English Pokemon website has revealed a silhouette of Darkrai. It appears that the official unveiling of Darkrai in North America will be soon. While an official announcement hasn't been posted yet, speculation is that it will be the Darkrai event for Pokemon Diamond and Pearl and/or a Movie 10 dub announcement.
Earlier this week it was revealed that the tenth movie manga has the title "Dialga vs. Palkia vs. Darkrai" which is the same title in Japan. This suggests the title will be retained for localization.