DC's announcement of their movie lineup for the next six years came out of nowhere and the inclusion of a Suicide Squad movie was perhaps the most surprising inclusion (aside from a stand alone Cyborg film). Even more unexpected was DC's decision to release this movie just months [Batman v. Superman: Dawn of Justice](movie:711870) and in the same summer as [Captain America 3](movie:994409) and X-Men: Apocalypse.
Ballsy move DC.
On the surface it looks like this decision was made after huffing a bunch of paint thinner. Dawn of Justice is just establishing their universe and the heroes that exist and then DC goes into a movie about a not-terribly-well-known group of criminals called the Suicide Squad.
This could, however, end up being a sneakily good idea for a few reasons: Deathstroke, possible video game tie-ins, and set-up for future villains.
Deathstroke is the resident bad-ass in the DC Universe and has a growing popularity of late. He was the main villain in the second season of Arrow, which introduced him to people who may not have known of him and reintroduced him to those may have forgotten about the Terminator. While he has been a recent addition to the [Suicide Squad](movie:2283363), he's been all over DC titles over the past few years. Most notably in Arrow and Arkham Origins. His fight in Arkham Origins is arguably the best part of the game.
That leads me to my next point, at the end of post credits of Arkham Origins there's a scene where Amanda Waller is recruiting Deathstroke for a team. This scene alludes to a Suicide Squad game that could be in the works. If its true that they're making a Suicide Squad game, then they could sync the release date with the movie thus capitalizing on the title (yes most superhero movies have half-assed games that release with them, but this is Rocksteady here).
The big reason why DC could've decided to do this movie so soon is to set-up the villains for their CU like their doing for the heroes in BvS. They could be using this movie to introduce characters like Deathstroke, Black Manta, Cheetah, Deadshot, and Harley Quinn who all could appear as villains in later movies. This movie is being considered just DC's attempt to capitalize on the popularity of Guardians of the Galaxy, but it could be so much more and just may very well be a huge movie in setting up the universe as a whole.