Will creeper world 4 be added to the Knuckle Cracker Universal Collection on steam?
Probably, yes, but you'd still have to buy it, since the price of the bundle will reflect the addition of the game.
Pricing and packaging decisions are only really firmed up about a week before the game is released.
Apologies for editing your OP. I fat-fingered and accidentally typed my response in there instead of replying.