Unsubstantiated, but someone on Reddit took a survey that appears to spill the beans on Mass Effect 4. It should be noted that the anonymous Reddit poster deleted their account shortly thereafter.
(Many details of Assassin’s Creed: Unity, Assassin’s Creed IV: Black Flag, Dragon Age: Inquisition, and Halo 4 were leaked in a similar manner as well.)
The next Mass Effect game takes place in the Helius Cluster (a cluster of 100s of solar systems in the Andromeda Galaxy), far removed by time and space from Commander Shepard’s heroic acts and the final events of the Mass Effect trilogy. You are a pathfinder, a combat trained but un-tested explorer leading an expedition into the Helius cluster to establish a new home for humanity. As you explore this sprawling series of solar systems (over 4x the size of Mass Effect 3), collecting resources and building colonies, you will encounter the savagery of untamed lands in the form of cut-throat outlaws and warring alien races. To survive and colonize the wild reaches of space, you will need to grow your arsenal, your ship, your crew and make strategic (and often uneasy) alliances to fight against increasingly menacing foes. Along the way, you will encounter the remains of a once powerful and mysterious alien race, the Remnant, whose forgotten technology holds the key to gaining power in this region of the galaxy. As you uncover who the Remnant were, and the mysteries their ruins contain, you are drawn into a violent race to find the source of their forgotten technology that will determine the fate of humanity.
More details at the link. There were multiple gameplay categories that were described and the survey taker was asked to rate their interest.