An unnamed and now deleted informant on Reddit took a survey for Mass Effect 4 that apparently leaked information on the game. Now, whether or not it was a legitimate survey is not verified, but a certain aspect of the survey falls in line with other official game surveys. If you answer one question a certain way, the survey ends for you — it was the same when we took the a Square Enix survey.
There's a lot of information to be found in the original post on Reddit (wall of text), but here's a summarized version:
The survey suggested that the next Mass Effect game is set to take place in the Helius Cluster, in a setting that is very separate from Commander Shepard and the events from the Mass Effect trilogy. The game will have you acting as a pathfinder, someone that is trained but not tested for battle on a journey to find a new home for humanity.
On you journey to colonize world (and you will be colonizing it), you come across the remains of the "Remnant" a once powerful alien race whose technology holds the key to controlled the region of the galaxy. Looking deeper into the Remnant leads you on a journey to keep the Remnant out of the wrong hands and save humanity.
Progression through the game will lead you to establishing settlements in the Helius Cluster, each settlement location is a strategic decision. Those settlements can offer you resources to upgrade equipment or give your crew more missions.
In the game you will build a crew of seven, each member has their own story (that you can explore and develop relationships with) and their own set of unique skills. Out of the seven companions, you can only take two with you on your journey.
Dialog with characters will build or destroy loyalty, and the choices you make will impact the game as it progresses — AKA choices matter.
The validity of all of this information is in question, but it is all very interesting none-the-less.