The coda is an extra, subtle layer of emphasis that this entire scene hasn’t been about Deadshot and his vengeance subplot with the guard, or even about Deadshot and Flag sizing each other up. What actually happened was a conversation between Deadshot and Waller, in which Lawton shows her what he’s made of while he shows her that he knows what she’s made of — and Waller does exactly the same.
It should go without saying that the extra layer of Smith and Davis’ casting on this scene — the fact that it gives two of the most respected black actors in Hollywood today a chance to play two black characters acknowledging each other’s power while ignoring all the other (white) people in the scene — is magnificent icing.
Floyd Lawton is white in comics canon, but Smith’s casting is no cosmetic change when he demands, serious as a heart attack, that if it turns out his daughter can’t hack it at an Ivy League university, than he would like them to "white people that shit." It’s precisely how you know that he really isn’t talking to Flagg — he’s talking to the only other person in the room who is what his daughter might some day be: a badass, powerful, grown woman of color.
That was a mesmerising scene. Truly a joy to watch.