I am saying this since years everyone made fun of me. Check my threads
Classic Oda move, tying things back to a scene or panel from the past, many years later. Of course, it could all turn out differently, but giving Koby an active goal now changes a few things.
Many people (me included) didn't believe in this Koby / Luffy rivalry after Marineford, when Luffy basically just once punched him. But a scene like that sticks with you, and you always wonder when Oda is going to address that again.
Doflamingo said it best...
We know Doflamingo would have lost to Kuzan even if he tried to fight, but the reason why he didn't try is more interesting to me. He saw in his Face that he's on a Mission, a determined Man. Those types are the worst enemies you want to fight.
Now we have to wait for the RAWs and see how determined Koby looks.