So we have three maps that feature the four current main characters, and each map links to the next via a nav card/card reader combo. Each card reader is located very close if not directly under the tower on each map.
What if these towers are being used to locate and/or power a fourth location?
Of course that raises that question of, assuming this theory is correct, whether the fourth location is something that we already have on disc and finishing all three Easter eggs on the same side and installing all nav card will unlock it, or it's simply the final DLC map. Of course if it's simply the final DLC it would seem that there would have to be a significant map difference to justify the massive lead up, kind of like how you couldn't do the moon easter egg without having done the COTD and shangra-la Easter eggs first.
What do you guys think?