These three commanders will be saved for last because they will be the strongest commanders.
Vasco and Devon got introduced first because they're the weakest (no, Burgess appearing in Dressrosa doesn't count), then you got mid tiers commanders like Burgess, Van Augur, Doc Q and Stronger then you got potentially the three most dangerous commanders (Shiryu, Lafitte, Pizarro).
I'm hoping that Shiryu will go to Wano and retrieve Kaido's and Big Mom's fruits. Would be cool if Lafitte infiltrates Mariejois again for the Lols. Dunno about Pizarro, maybe he will claim his old country back in the North Blue?