So Kid took what he wanted, stole the RHP and left. He didnt cared for BM at all. She Never was a goal from him. But he left Snack alive, just for the sole reason of humilating Big Mum.
Conclusion: Kid didnt cared for the Yonko itself, except for Shanks.
Kidd's also honest. If he told Snack he'd trade his life for the Poneglyph, Kidd would keep that agreement.
Kidd being stronger than Luffy pre-Wano is kinda crazy, considering Luffy literally had 2 years of Haki training with Roger's Right-Hand.
IMO, I always said Kidd's biggest issue is purely Haki (Law has similar issues).
Kidd with Giant Haki skills like Linlin has will be a huge problem to deal with.
This is great for Urouge, too; my man is being linked to Kidd, who now has a 3 Billion Berry Bounty. Urouge was last seen in... Balloon Terminal, further connecting him to Sky Islands.
IMO Urouge is either in Heaven World, or will go there, and Kidd is trapped in some section of the Underworld, with a prison similar to the ice prisons in Impel Down level 5.
Possible Kidd is trapped in an ice prison, like the reforming Ice in the Jewel Ice Sheet:
https://onepiece.fandom.com/wiki/Jewel_Ice_Sheet