I believe Luffy gonna meet Sabo on Next Island, so Sphinx Island makes sense, however with Kuma being there too, things gonna get complicated
SHs and Revos gonna exchange what they know and decide where to go next (Morley can lead a Group to Elbaf, while Lindbergh lead another Group to Vegapunk Island, while Karasu can act as Messenger in between or go back to Dragon ... etc)
However Kuma gonna get Remotely Controlled and use his Powers to send SHs with Highest Bounties (Monster Trio) to different WG Locations
Zoro sent to Impel Down, Sanji to Vegapunk Island, Luffy to Mary Geoise