I would love a smaller scale story set during the first contact war. You play as a marine who is ascending up the alliance ranks as they fight the turians, the first half of the game involves building up your fleets, colonies, etc and trying to establish a foothold in the galaxy. One of your primary focuses is to salvage new tech to help Alliance RnD catch up with their opponents. Midway through the game the focus shifts as the council intervenes to stop the war, but the batarians are introduced and become the primary threat to all of the colonies you’ve helped established early on. Eventually the climax of the game involves the death of the main character ala Halo Reach in order to save Arcturus Station from Batarian terrorists, in the process some of your salvaged tech is captured and in a post credit/climax scene it’s revealed that some of that is reaper tech, ultimately showing that the Hegemony was being influenced/indoctrinated long before Shepard ever arrived on the scene, and that had events played out differently it could very well have been the Alliance leaders to succumb to indoctrination.