The change to Koggy's W will be an early game buff
And a nerf once he gets above 160 attack damage, or any build with Rageblade and Bork in it.
The much much much larger nerf Koggy is suffering this coming patch, however, is the change to Fervor of Battle. Kog will no longer be able to pre-charge the Mastery on minions or towers and then switch targets after popping W for a significant hike in his damage output. With most ADCs taking Bloodlust, that means Kog previously could get a nice damage advantage over them before Crit came into play.
With the change to Fervor, Koggy's new W base damage is more or less a neutral change. I suspect he's still going to need quite a bit more work before he begins to approach the power of the game's untouchable golden-girl hyper carry.