Icon Of Sin Doom
The Icon of Sin is the main antagonist and final boss in Doom II, TNT: Evilution, The Plutonia Expirement, and Final Doom. The Icon of Sin is a gigantic, grotesque head of a demon embedded on a wall. It's forehead is open, exposing it's brain.
Icon Of Sin Doom 2016
After it was announced that this game is going to be like Hell on Earth, many poeple speculated that the final boss is gonna be the Icon of Sin. This makes sense at first, considering how the last boss of Doom original was the SM, and in Doom 2016 SM is the final boss again.
Icon Of Sin Doom 3
But many people do not remember that we actually MET IOS already in Doom 2016, and it was dead.
Here is the info: http://doom.wikia.com/wiki/Icon_of_Sin_(Doom_2016)
So, unless this was just a silly easter egg, we will not fight the IOS.