There should not be another Mass effect in the "numbered" series unless it follows the exploits of Commander Shepard.
But in terms of a AAA game in the universe? I don't know. Nothing after the ending makes sense, the universe is effectively ruined, and Nothing interesting happens before. Sure you have the First Contact war but that has not only already been delved into in other media, it is a frankly boring story and I don't want to shoot at Turians.
But in terms of a AAA game in the universe? I don't know. Nothing after the ending makes sense, the universe is effectively ruined, and Nothing interesting happens before. Sure you have the First Contact war but that has not only already been delved into in other media, it is a frankly boring story and I don't want to shoot at Turians.