Kog'Maw is still good.

The and buffs help him quite a bit as an adc.

AP Kog I think is pretty awful though.

you mean as AP? he's incredibly powerful

As AD he's mechanically intensive but still pretty good late game, build wise is a bit odd but in the end, range > all

Hes viable, its just that most people seem to be playing ap kog instead of ad kog, the change was to encourage more people to play ad kog.

At least that's what it looks like.