E-Day would be "interesting to explore" said Joshua Ortega, former writer on Gears of War 2, in a recent interview withX-One:
"E-Day would be a really interesting one to explore. It has a lot of emotional impact, it was the day that Dom and Maria lost their children, when humans had been fighting humans for so long. The war was finally over, and then they had to take up arms against a greater threat. I feel like that’s the most compelling gap to fill for sure.”
Ortega isn't writing for the Gears of War franchise anymore, but E-Day - which stands for Emergence Day - would make a lot of sense. It'd give the player a real sense of struggle as an almost endless horde of enemies bashes your army further and further back. Alternatively we could see Black Tusk aiming for a series set during the Pendulum Wars, which would give them the ability to create multiple sequels.