Mac Walters can't go into specifics, but he can talk about the last game's ending.
"We have agreed to tell a story that doesn't relate necessarily to any of the Shepard events at all, whatsoever," says Mac Walters, Mass Effect's writer throughout the series. The next game absolutely has to feel like Mass Effect, look like Mass Effect, but cannot be a Mass Effect spin off. Don't expect to see Shepard or any of that character's companions; the next game has its own story to tell.
Story telling is much on Walters' mind, particularly after the fan outcry that followed after the end sequence in Mass Effect 3. Walters acknowledges that the development team underestimated the level of ownership the fan base felt it had over the character. "I'm not saying that our decision was wrong or right," says Walters. "I think we just underestimated the impact that would have on certain players." It's a lesson learned, says he. Now it's time to go forward, not dwell on the past.
But if you were hoping Walters would say a little more about what the next Mass Effect would be about, rather than what it wouldn't, you're out of luck. We just know it's coming; we don't know what it is.
Source: Complex Gaming