Big, open world survival extraction shooters unfortunately come and go, with very few staying around long enough to be consistently played on a major scale. DMZ being linked to MW4 is a good way to get a easy advantage in that sense. However they need to do a lot right to keep a player count going.
The mode needs more PVE stuff. MW2 had a good grasp on that with new bosses, new world events etc, MW4 needs to follow the same vein. I'm not saying drop everything update one, however they need to consistently push new missions/story/objectives into the mode.
Along with that idea, when we get the map expanded (I believe we may be moving north into Russia more in the map, then the part of the map with South Korea really should go to just PVE. Reduce high level loot drops and enemies, make it like a staging area without any feeling that around the corner you can get shot by a exfil camp.
Even something as simple as having a mission where we clear out a couple of strongholds of NK fighters to loosen their hold could be put in to explain why SK has turned somewhat safe again.
Overall, the mode has potential, and it has the legs to really push forward. But we need small changes, nothing gamechanging and consistent yet engaging updates to the world to avoid stagnation and eventual player drop off.