With so many big shots making their moves, I feel it's just a matter of time (a few chapters, probably) for Hancock to take action.
And, well, she has no other group to ally for but the Straw Hats.
I feel she's already coming to Egghead. Last time we saw her, she was contemplating leaving Amazon Lily because her presence there would endanger the Kuja.
While it goes into a gag of her wanting to marry Luffy, I don't think she has any way to know where Luffy is.
So, why and how would she come to Egghead?
It's simple. In that same chapter, we and the Kuja are introduced to the Seraphim. They are the ones most responsible for the damage done to Amazon Lily.
At the end, Hancock was hearing how one of the Seraphim looked just like her. We see her lost in thought about the matter.
So, destroying the Seraphim would be a way to keep Amazon Lily safe even after Hancock leaves.
But she has an even stronger reason to seek the Seraphim and their creators: S-Snake is, for all intents, a slave version of Hancock. She would not allow such travesty unpunished.
As such, she's not coming for Luffy. She has no idea Luffy is there at all. She's coming for Vegapunk.
But, how is she arriving? Would she bring the Kuja to the New World? It's possible, but I think the story is setting up another way. I believe that Hancock will be by herself when we next see her.
The key for her arrival may be with Sentomaru!
We saw, both pre- and post-timeskip, that Sentomaru and his Pacifistas were frequently stationed in Sabaody Archipelago. However, he was also Dr Vegapunk's bodyguard.
That implies that there may be a fast way to move between Sabaody and Egghead. Maybe an underwater vacuum rocket system?
So, back to Hancock, who was her with last time we saw her?
That's right: Rayleigh and Shakky, two of the most crafty residents of Sabaody. If anyone could point Hancock how to quickly reach Dr Vegapunk to seek answers about the Seraphim, it would be them!
So, don't be surprised if at some point in Egghead we get a mysterious unexpected arrival.
If that happens, my bet is clear: Hancock has arrived.
I feel that scene with Sentomaru releasing the Mark III Pacifistas is a prelude to that. At some point, he will get word of their transport system being used to bring people from Sabaody. He will assume this is an early marine force.
It will be Hancock instead, and we will get a scene that calls back to a certain moment in Marineford, it's just this time Sentomaru asks why she's here since she's now an outlaw, and Hancock furiosly inquires "where's Vegapunk?".
If you are doubtful of Hancock's arrival in this arc, I first will point out how every major player is moving into position for the endgame. She, like Kid, Shanks, Law, Blackbeard, Crocodile, Mihawk and others will have to make a move, and finding the Straw Hats is the most likely outcome.
Second, we are dealing with the Seraphim now, and the Straw Hats have history with Kuma, Jinbe and Mihawk, making the confrontation with those Seraphim somewhat personal for them.
No one questions the potential of Zoro vs S-Hawk, or that fighting S-Bear "bears" the weight of fighting Kuma, or that Jinbe shouldn't confront S-Shark.
That same connection is lost with S-Snake. She's an unknown entity for most of the crew save Luffy, and Luffy will likely be busy with the main villain.
So, I feel a Hancock herself will confront S-Snake, just like Jinbe is likely to confront S-Shark.
There's also the thing about S-Snake's powers. There's no one but Hancock to explain them and show how to counter them. I believe her powers have lots of secrets, and we will need Hancock to fully counter S-Snake.
What happens with Hancock after Egghead is something else, but I feel more strongly than ever that her placement in the T100 Colorspread was not just random happenstance.