After the negative response to Batman v Superman: Dawn of Justice, Warner Bros. went to drastic measures to change Suicide Squad's tone. The studio enlisted a company known for editing trailers to jazz it up a little (hence why we got so many of those stylised cutaways showcasing Task Force X's abilities) and drastically changed the final act in a bid to lighten up the ending.
Originally, The Joker was going to track down Enchantress after his helicopter crashed, making a deal with her to turn him and Harley Quinn into the King and Queen of Gotham City. However, as he actually threw her out of that chopper in response to her caring about the rest of Task Force X, she had a change of heart by the final battle, and ultimately rejected her Puddin'.
Now, though, director David Ayer has revealed that the original plan for Suicide Squad was for the movie to end with Harley romantically involved with Deadhsot instead of the Clown Prince of Crime.
He also explains that Diablo was supposed to survive, but all of this changed during reshoots. Why the change? Well, Warner Bros. may have decided that Harley reconciling with The Joker was a "happy ending," and them ending up together was probably meant to set up the scrapped Joker vs. Harley Quinn movie.
Check out Ayer's comments below: