Epic Games revealed that there's a unlockable second campaign in Gears of War: Judgement. If you unlock every star by completing certain parts of the main campaign by doing special stuff like headshots, gibbing, without dying, etc. you'll unlock it. So aside from sounding like DLC you have to buy, it sounds like a nice not so secret unlockable. It ties into the Gears of War 3 campaign in a part you can read below,
"Obviously we don't want to give away too many spoilers in how it's going to end or what you're going to see," Lead Level Designer, Jim Brown added, "But the basic gist of it is that when they're at the fort, Marcus sends Baird and Cole off to find supplies and reinforcements, and then he goes off to Azura. Then at the very end they show up with helicopters. This is where they went and what they did on that mission."