Step 2: Hard-R all the way. The moment they heard that a Deadpool movie had been greenlit they should have suspended all but R rated scriptwriting for Squad. Let Fox test the waters. This Squad is very uneven in tone and mood with PG-13 here and hardcore mass murder over there. Brutal and insane with as much dark comedy as possible.
Step 3: Character/story structure. WB-DC did it to me twice within a few months. I was sold on a Titanic struggle between B&S, and a wild group led by and centered on Joker and Harley.
It could have had the four character archetypes and the other-worldly and mystical super threat found in Ghostbusters and, indeed, ANH. But it would have tremendous insanity and criminality ladled over the top. Great passions and instabilities.
Han/Peter/Joker, Leia/Egon/Harley, Luke/Ray/Deadshot, and Ben/Dana/Waller. Utterly twisted and bizaaro world versions of these types. H/P/J is self-involved and sardonic and skeptical and always wise-cracking and quipping, L/E/H is analytical and clinical and practical while incredibly toying and manipulative, L/R/D is the heart and soul though murderous, B/D/W is foreseeing and alert to the threats and driving for the solution while joining the group a bit later than the others and brutal in her methods. Joker and Harley would be out front throughout and there would be versions of the droids and Chewie and Moranis and Hudson and Genine and the X pilots.
Davis could definitely handle it and I believe Robbie could play her expanded role very well. The Joker would require someone very skilled with black humor, genuinely funny. If Leto would have difficulty, I would have cast with male-model headshots and high school yearbooks until I found someone with the right physical qualities and a natural gift for sardonic wit. Smith was the best part of this PG-13 version. Nobody can do Will Smith better than Will Smith. But Will Smith is very PG. I missed him in ID:R. I wish he would have gone there and used his personality and clout to fix that film. I’d have cast a hard-R menacing badass instead.
Step 4: Logical and sensible within it’s fictional universe. Why not call in Batman and Flash? Waller could learn that the outside threat deals very harshly with any power that dares to oppose it. Plausible Deniability. They assemble a team that no responsible authority would ever entrust to do anything. Officially they act entirely on their own.