Recently, a person on Reddit claims to have taken a survey that contained details on the plot, gameplay elements, etc. for Mass Effect 4. While many are skeptical on the validity of the claims, people have noted that the same thing happened with Dragon Age: Inquisition prior to its full reveal, and the details that had been leaked turned out to be true.

The details provided can be found here for those curious (not posting them in the thread because some may not want to see possible spoilers, and I'd just be copying & pasting everything).