He's going to lock in so that we will get one final chapter of Zoro vs Sommers after Sanji vs Killingham finishes.
There is no way Oda offscreened the fight with Zoro not even using a named attack. Especially when we saw that Sommers(with Imu's gifts) has the ability to match Zoro's power. What I'm guessing will happen is much like how Imu caused a personality change in Harald and Shuri, he will do so to Sommers as well.
Since Gram is based off wrath, all Imu needs to do is just change sommers's personality to make him wrathful.
Sommers in of himself is a bum. But Imu can turn him into a powerful weapon.