I don't know If anyone has found this yet, but I was walking through sector 5 when I noticed that all the doors in the area near the place where the rookie first starts were opened. Curious, I wandered inside, and found that every door that had something behind it was open (open as in gone, like the secret door, not just openable). This leads me to believe even more strongly that the secret door is no more than a loading error. Doors to rooms that Bungie simply did not use. I have not yet found the trigger that led to these doors failing to load, but I had just traveled from sector 6 through sector 8.
The more I see these kinds of things (missing doors, missing Optican booths) the more skeptical I become.
Video in fileshareIf you look around the rest of the area, you can see a couple of other doors that have also failed to load.