Early information suggests that the project would be more of a reboot than a direct sequel to David Ayer's 2016 feature, which was met with less-than-favorable reviews upon its theatrical release.
According to Variety film reporter Justin Kroll, there's another reason why O'Connor is no longer behind the helm: his story for Suicide Squad 2 apparently "ended up being nearly identical to the Birds of Prey story". The project doesn't have a release date yet, but is expected after Cathy Yan's Birds Of Prey, which is scheduled for 2020.
He continued: "Yeah it was a big fun silly movie".
That said, Gunn probably won't run into the same problem that O'Connor did when writing his script for Suicide Squad 2. Nothing but originality from this guy.
Gunn's witty, irreverent sensibility turned Marvel's Guardians of the Galaxy from little-known minor characters into one Disney's most acclaimed and bankable franchises. Gunn is taking a new approach to the property and this isn't exactly a sequel to Suicide Squad. A move to DC-which is in desperate need of creative direction-would be a definitive middle finger to Marvel for letting him go, and Gunn's sensibilities would actually be ideal for the bad guys forced to do good of Suicide Squad.