If they continue to go canon in future games, I hope they include some of the early stuff they probably skipped (Kuro arc, Morgan arc, Davy Back, Amazon Lily) Along with the new stuff from Dressrosa and beyond, I hope they continue to beef up the beginning and mid-sections of the game.
They're already going whole hog on showing Dressrosa characters that have since showcased only a fraction of their abilities (Sabo, Doflamingo)
Though considering how few characters become playable and not even recently popular characters like Monet aren't (likely) to be included, I don't think they will really incorporate THAT many Dressrosa characters. Barto and Cavendish are the most likely. Kinemon will also be included eventually. Rebecca & Kyros might be support. Some characters like Baby 5, Senor Pink, Trebol and Diamante may be included either as NPCs or playables (almost all DD family members will likely be NPCs) the rest of the foreign gladiators will be lucky if they even appear in a future game at all
Pica definitely won't and will most likely serve as an Oz-like boss. Too unique to Dressrosa's terrain
The collosseum I don't think will follow the canon story that closely though. Will probably have Luffy fighting random boss NPCs that weren't in the arc then jump directly to bearded Sabo fighting the
What would really be sweet if they dared to include Leo as a playable character. Give him the same walking speed as Luffy (or faster) and he'd be near untouchable aside from AoE attacks. Plus there'd be the added amusement of playing as a fly-speck taking down entire armies, perhaps with an ability to summon a swarm of the little buggers. Would also be a good way to incorporate NPC tontattas hordes into the game.
Bon Kurei and Wapol would argue that point. And they've been there since the first one!
And are also the two characters I most want. I think I'll be skipping this one unless it hits the magic price point of 15$ or less on a sale like 2 did.
Yes, especially Wapol! Been waiting to finally have the chance to gobble up entire armies with the true Pirate (Hippo) King.