Koggy would be a significantly more effective Tank-Buster if his W and R did physical damage
Just grab some armor pen runes, run TriPen, and shred 300 armor down to 50.
As an added bonus, grabbing Manamune would allow him to get all the benefits of the AP build without gimping his auto-attacks. Sure he would be losing out on Athenes, but is losing out on Athenes really that huge of deal at this point?
Probably wouldn't ever happen, though. Kog doesn't have nearly enough dashes to make flashy-dashy plays.