I think Kog's W should be balanced around letting him move while attacking

Not at 100% movement speed but just enough that he isn't rooted to the spot so that he can dps with similar uptime without scripting. Example: Kog'maw can now move while attacking for the duration of Bio-Arcane Barrage but also has his base movement speed lowered to 110/135/160/185/210 for the duration.

With this change, the variation depending on human error drops dramatically even highly skilled Kog players will have moment where they clip autos for a few tenths of a second too long too frequently and lose a significant portion of their dps. By reining in this variation, Riot doesn't have to consider dramatic edge cases when looking at Kog's dps and can balance more easily.

It would also hammer in the 'walking turret' theme Riot and Kog players want.