Dignity. Always dignity!
From update 1 Poots says that the gold smoke knight is the true end boss.
Does this mean we will never see the king? Is it too powerful? Or will it be an alternate campaign expansion?
Only Adam knows. But from his message during the Lantern Festival cancellation, it sounded like he foresaw the King as being part of a more complex expansion or a new core game.
He has all the plastic made for the monsters and figures, so I highly doubt he's going to let it go to waste. He likely hasn't determined what exact form the King will take, but I practically guarantee it will not show up in this campaign.