It has been announced that Lego and Warner Bros. have fast-tracked a spinoff based on The Lego Movie starring Batman. The animation supervisor from The Lego Movie, Chris McKay, has been set to direct. With Seth Grahame-Smith (known for Abraham Lincoln Vampire Hunter, and Dark Shadows) as screenwriter. Will Arnett is back as Batman, and Roy Lee, Dan Lin, Phil Lord, and Christopher Miller back as producers. The presumed release will be in 2017, which is probably pushing The Lego Movie 2 into 2018.
In the mean time, check out this video of Batman getting ready for his role in The Lego Movie. Maybe he will be more prepared for his film.
It was The Hollywood Reporter who first reported on this Lego Batman Movie: http://www.hollywoodreporter.com/heat-vision/lego-batman-spinoff-movie-works-738631