I want "Mass effect; Retro"
Imagine; the galaxy set before humanity became a council race, when Shepard wasn't a Spectre and the biggest concern was pirates and slavers, where the Geth, Batarian terrorists and Krogan warlords were the real threats to galactic peace and prosperity.
Making sure these threats are contained, the council sends out teams consisting of the 3 council races, plus humans trying to butter the others up for a spot on the council, onto planets containing these threats, to board ships and free prisoners and materiel. Commandoes from every council race, working in the shadows to maintain peace and put out the fires in the galaxy before they can spread.
Something like Mass effect 3's multiplayer meets Fallout tactics. You recruit your teams, try to have a mix of tech, weapon and biotic specialists, do open assaults or covertly sneak in, you manage the abilities your squad has, replace those you might have lost, equip them with the weapons they might need while paying attention to how many credits you have access to...it would be fun.
Heck, a turn based tactical game seen from above sounds kind of cheap to make, yet add a map editor where you can add whatever enemies you want and can upload it online, and a co-op and versus online game where you can test various set ups of a team versus another player and you have a game that sounds both enjoyable and long-lived.