It doesn't make sense for Koby to face Kuzan. Kuzan objetive is probably the world goverment (Imu?) And he's using BB to get closer to the OP to achive that goal.
If Garp was dead, I can see Koby trying to get revenge for what Kuzan did, but he's just a prisioner.
There are more chances of a Kuzan vs Smoker exchange than Koby vs Kuzan. At least Smoker has a conection with Kuzan.