I suspected Hancock might get captured since the beginning. She has too much background with the Celestial Dragons for Oda to have missed this opportunity
But it's not necessarily a play on Coby or at least not alone. The last time we saw Fujitora, his ships were assaulted by sea kings, sea kings which are majoritarily seen in calm belt
Amazon lily is one of the few islands located in Calm Belt
So Fujitora might have attempted to reach Amazon lily at this point
But then again, it can also appear that seaking can be located somewhere else(remember the first sea king we saw was appearing in East Blue), but it's still important to note regardless
And ability-wise, considering Fujitora is blind, it makes Hancock's primarily hax ability useless and his gravity is ideal to capture people
On the other side, Oda did decide to focus on Coby for some reasons, and he is bound to become an admiral, on his way to prove himself further, so i assume, he might also play a role in something or at least get some kind of credit into this
Maybe though Oda just wanted to create an affinity between Hancock and Coby through this at one point