Unpopular opinion...Kog'Maw is in a good spot right now
Looking at his win rate, Kog'Maw appears to be in a pretty health spot right now, despite some pretty big changes (aka nerfs) that happened recently. He can't go full attack speed like he used to, but let's not forget that even without a ton of attack speed kog maw still has a lot of range and armor shred. And with some slight changes to his build he seems to be doing well in the current meta.
TLDR don't buff Kog'Maw. He's in a good spot.