This has me wondering as well.
I bet we will see Marcus again. Gears and his character are too popular.
Pendulum Wars, battle at Aspho Point with Marcus, Carlos Santiago, Helena Stroud, Bernadette Mataki and Major Hoffman leading the Spec-Op troops- including Dom and the Pesangas- to recover the Indie scientists and the Hammer of Dawn technology for Adam Fenix. Not to mention being able to back-track over an 80 year war to popular battles like the siege on Anvil Gate with Lieutenant Hoffman. Or even further the story of the original trilogy and have a game that follows the Locusts from their plans for E-Day, up to the Hammer of Dawn strikes. Endless, and awesome, possibilities!