Sabo, Fujitora, maybe even Law or Kid.
Him and Sabo are opposites to each other in what they believe, have already fought, Sabo’s Dragon’s right hand and Ryo a massive Akainu fanboy. Sabo was introduced as Flame Emperor the same chapter we saw Ryo go on his mad rant about how perfect the Celestial Dragons are.
Him and Fujitora have been tied together as the new Admirals but both have extremely different views on the World Gov
Law/Kid have the same animal references as Fuji/Ryo so it might be a way to give each a solo top tier to beat, cause otherwise there isn’t anyone for them and they peak with Big Mom.
He came to Wano and didn’t interact at all with Sanji so that’s not much to make me think he’s Sanji‘s EoS villain. Same with all the Admirals, none of whom have had any meaningful interaction with him.