Mordekaiser, Pantheon, and either Kayn/Kha'Zix/Nocturne/Pyke/Shaco/Talon/Zed.
I'm going to rule out Kayn and Zed due to recent patch notes involving them, leading me to think the champion designs are fine and just need numbers adjustments.
Kha'Zix has had virtually the same kit his entire existence and seems pretty fairly balanced. Also received the Worlds chromas last season so this makes me think there's not much attention on him.
I also don't think it's Pyke just bc he's new compared to the other champs on the list and he has seen a little bit of patch notes attention. Also doesn't need any visual updates.
That leaves Nocturne, Shaco, or Talon. I'm gonna lay my bet on Talon since the E is a pretty wonky ability and he hasn't gotten much visual love in a while since the assassin rework. Also he's not too popular.
Nocturne is a pro staple and Shaco had that weird box rework thing. I wouldn't be surprised if it was Shaco though.