From ca3's blog: (I don't watch Super Sentai so forgive me for getting some related terms incorrect)
A crossover between 40+ Riders and 200+ Sentai. The dream plan has finally come to celebrate the anniversary! The main story plot is created because of the 'Heisei Rider 10th anniversary project'. 'Kamen Rider Decade' which featured nearly every single Rider in history, will have a big fight with Gokaiger, who transforms to various Sentai in history and is the 35th anniversary project.
Of course Fourze, Den-O with the Imagins, and the new Sentai starting from February 2012 will also join the movie. From now on, there will be regular Spring Hero Movies!