Buff AP Kogmaw, or make him full AD
Seriously, kogmaw is not viable as an ADC right now, and honestly it was always his least fun iteration. How about instead we buff his ap ratios on his base abilities and remove the execute from his ult and give it back a slight range buff, real AP ratios and base damage?
If you still want kogmaw to be a viable auto-attacker then make more AP items that buff the nashor's tooth AP on-hit playstyle, don't punish kogmaw just because people whine about his range and spammability, there are more than enough ultra mobile champs in league that artillery platform kogmaw shouldn't be that much of a threat to them. Kogmaw is quite possibly the least mobile champion in the game right now, he deserves a playstyle that lessens that weakness.
Alternatively, give him straight AD ratios across the board and make his void ooze last longer and give him a move speed buff while he's on it so he has some chase. If you were to make him full AD I'd make his playstyle more about applying DoTs with his abiltiies and chasing people down with the HP shred, instead of just having a bunch of upfront damage. Make his Q splash to nearby enemies on hit and give it armor shred over time and his void ooze deal it's damage over time as long as the enemy is standing in it and give him a movement speed roid on his death passive to secure kills. Make his ult do low on hit damage but apply a slow and damage over time, increasing based on missing HP.
Either iteration would make kogmaw way more fun to play, right now despite being one of my favorite champs of all time, he's so weak early he's basically unplayable mid and if a support CCs you, he's dead.
Kog needs some help in one direction or the other, but he needs help regardless.