The way I look at it, Doflamingo was someone that first brought up the term Justice after the CO9, so I think Oda was alluding that they have similar viewing points, though not as ruthless, I think Doflamingo hides his action under Justice. "Justice will prevail" is a term they both used I think. Not completely similar, but I think it is fair to say that it unites them a bit, unlike other villains that do not have that much in common.
this is the whole quote.
Pirates are evil? The Marines are righteous? These terms have always changed throughout the course of history! Kids who have never seen peace and kids who have never seen war have different values! Those who stand at the top determine what's wrong and what's right! This very place is neutral ground! Justice will prevail, you say? But of course it will! Whoever wins this war becomes justice!
lucci and DD is as different on their views of justice as day and night.
well to the topic at hand. that could be lucci but there was many chars. that wore the same type of hat. for example WB 5th divison captain Vista. resemblence is there. though will WB remnants use a wepon of mass destruction is another issue.
there was also the laffitte from BB.the hair is a little different but that could be the shadowing.
or could be that mafia boss like supernova forgot his name.
though could simply be some1 we know that just bought a hat or some1 new
though every1 seems to think old enemies will resurface but i am not sure we will see some of them. my bet for now is crocodile, buggy(i know right even i cant believe i wrote his name), spandam (he hold grudges that man), and bonney (she does have a bone to pick with zoro and lufy) oda drew her when he draw other supernovas so it could be something.
Well, CP9 might really appear in the plot at some point, especially since Oda normally gets old characters back in plot like he did with Buggy, Croc and Mr.1, so I do believe they might come back.
The question is when and under what sicumstances. I doubt they will become pirates. It's against their sense of justice. I believe they might have become a group of mercenaries or either they might have joined Revolutionary Army as someone said.
Still there are two possibilities. Going by the silouette it might be either Lucci or Laffite.
Well, it might be like this...
I believe Ao Kiji might have joined Revolutionary Army, so if CP9 joined him, then they would be in RA as well.
Though they might be an independant group of mercenaries in New World.
Makes even less sense then being pirates imo, especially since the WG was holy for the CP9. They also were not betrayed by the WG but by Spandam, little but important difference. I think they are bounty hunters along with Kuzan.