Let me cut to the chase:
After you achieve the Death Machines after releasing the voiceover, there are two possibilities after getting them. NextGenTactics has said that the death machines are the 'reward' and nothing can be achieved afterwards, and even debunked a few theories. But here's one:
1) After getting the death machines, everyone goes and uses the nearest lunar lander. It could take you to an unknown place, because when you use them, you have an aerial view of Ascension. There are 4 lunar platforms, but a bit away from the map, in the distance, there is what appears to be a 5th lunar lander area. Maybe you need the Power Node Mystery completed to go to this mysterious place.
2) Some say that the death machines can become Pack-a-Punched and turns into the 'Godfinger'. However, I have searched MANY different places, and cannot find any video evidence.
3) If you look at this whole thing in a certain way, there is ties to Vorkuta. For example, there are 4 steps in the Power Node Mystery to achieve death machines. In Vorkuta, the fifth step is 'Raise hell!' and death machines are used by Alex Mason. This could be the fifth step, although it is Step 7 in the campaign mission. Step 8 is freedom, so could this be a reference to finally unveiling something about the entire zombie storyline, like Samantha being revealed or something about Gersch or Richtofen, an he mentions some questionable things during the course of a game.
I can't try any of these, as I don't have xbox, so can someone please debunk this for me?