I doubt that Izo would be shocked by one of the scabbards being defeated, they all are ready to die fighting Kaido.
I bet that is someone arriving, pehaps BM with Marco defeated, but its more likely that is someone that we are not expecting, probabily from outside Wano, as Izo is the one scabbards that know more about the outside world. Just expected that is not that Weevil guy.
Its why I've been saying the potential Ace finally. To have Izo react is unique because he'd be the only person familiar with the name "Ace".
If its not a Kaido transformation or something similar, here are my points for this argument:
- It being Blackbeard/Weevil doesn't work. For them to arrive, slip through all the chaos unnoticed, and be present for the Scabbards/Kaido makes no narrative sense.
- It "could" be Kanjuro, Orochi or some other villain (Jack, Queen, King), but I don't see how that would warrant Izo reacting the way he is. Unless it something like a hybrid Calamity. On that note, Queen and King are busy defending the dome opening, they shouldn't be there.
- Something ridiculous like former Rocks pirates are possible but Izo should not be familiar with them.
- It being BM would be way too quick considering last chapter. I doubt she'll be up there any time soon and the battle may shift to somewhere else anyway.
- It can't be a good character either considering Izo's reaction.
This is why I believe its either Kaido showing off unrestrained power OR its something Izo recognizes, like the name "Ace". Remember these people are prepared to die. I don't even see Izo reacting that surprised to Kaido. His former captain was Whitebeard, he SHOULDN'T at all be surprised by Kaido's strength.