Warner Bros. and DC released a joint press release:

Based on the popularity of The Lego Movie, and in particular the audience response to the depiction of Batman in that film, all future adaptations of DC works, including the upcoming Justice League film, will feature the iconic DC comics superheroes and villains as Lego characters. As part of this initiative, the next season of the hit WB television series Arrow will be the first to be Lego-ified. DC will also be rolling out a Lego DC Heroes comic line for younger readers.

Warner Brothers has released a proof-of-concept trailer, which can be viewed here.