I would think the Guardians of the Galaxy fanbase would have more interest in sci-fi aspects of that franchise.
This seems more like the ol' war movie with a messed up ensemble behind enemy lines. Like Tropic Thunder and Battlefield: Bad Company (r.i.p. in peace) parodied.
GotG was close to being Star Wars' Galaxy Quest.
Sticking Batman and The Joker in this movie is really brilliant to rope people that are just Batman film fans in, especially being more than just a Nick Fury stops by to chat cameo. Assuming the film is good and then gets people to try less popular future ones. Like oh, I don't know, Cyborg's film.
I think after the initial introduction films D.C. would be better off thinking about doing team-up films than more individual ones like Marvel is doing before heading back to an Justice League/Avengers collective film. Especially to prop-up the lesser known characters by sticking Batman or Superman or The Flash along for the ride. Like the old Brave and the Bold comics, or Green Lantern/Green Arrow, or the Batman/Superman book, etc. Marvel's started to do this, but still under the banner of...well, under the banner of Captain America really is about it.
And I'm not saying this just because it seems the most plausible way to get a Blue Beetle/Booster Gold film.
I thought FOX should have salvaged their Fantastic Four franchise by attaching it at the hip with X-Men for a film or two rather than whatever the fuck that last film was supposed to be. There's enough crossovers to mine for that.
If Suicide Squad does well, then they could also use it as like a "team up" with The Teen Titans in order to launch that who probably nobody knows outside of Robin. (Another Batman bonus!) Just do it like both teams trying to accomplish the same goal, whatever it is like maybe fighting Deathstroke, only, you know, with slightly different methods.
Unfortunately from that Snyder interview he said they just figured out what to do with Justice League after BvS and nothing really beyond this first wave. Marvel's at least got that nutso 20 year plan (from Iron Man forward) to at least help tie all this stuff together better. The Avengers -> Civil War -> Infinity War -> Planet/World War Hulk. (Okay...that last one's just me.) Maybe Johns has a better idea of what they'll be doing after he gets his Cyborg movie.