I thought BB wanted the world to be engulfed in piracy and evil, so without WG and Marines?
Lot of talk/hot air from him as per usual as it seems.
This chapter he made it clear that he wants to become official royalty under the WG. Same way Doflamingo blackmailed them into accepting him as royalty under their flag again.
Make no mistake, he loves piracy and some evil shit here and there, but overall it seems that he's comfortable with the PK title, chilling on pirate island doing whatever he wants and not having to go up against the WG (actually being a "well respected guest" in WG circles as royalty, too).
This chapter makes it seem very unlikely that he ever wanted to truly challenge the WG or Imu themselves.