If you were hoping that the good ending which sees Commander Shepard survive was going to be revealed as canon in Mass Effect 4, you're going to be disappointed. Similarly, if you were hoping for specific details regarding Mass Effect 4, you're also S.O.L. That was at least what I gleaned from ME 3's lead writer, who recently spoke with Complex.
It seems that no matter what you had your own personal Shepard do, the story of Mass Effect 4 will have nothing to do with what transpired in the original trilogy as a result of Shepard's actions.
Said Mac Walters, "Well, I can't get into details, but the idea is that we have agreed to tell a story that doesn't relate necessarily to any of the Shepard events at all, whatsoever."
"That's what we've been deciding for a while. But throughout it all, one of the key things is that it has to be Mass Effect. It can't just feel like a spin-off. It has to feel like a Mass Effect game at its heart, at its core. Just without the Shepard character or the Shepard specific companions."
There's been a lot of talk about the new Mass Effect game, but without BioWare saying much of anything. At this rate, we don't even know if the new game will take place before or after the events of the first three games, hence explaining Shepard's absence. The only solid thing to go on is that for good or bad, Commander Shepard is completely MIA.
The new game is even being developed by a new team, with additional help from the Edmonton branch.
Wrote Community Coordinator Chris Priestly, "The way our games at BioWare Edmonton/Montreal work is that there is always a core team. So there is a core Dragon Age team (Mark Darrah, Mike Laidlaw, David Gaider, Matt Goldman, etc) and there is a core Mass Effect team (Casey Hudson, Preston Watamaniuk, Mac Walters, Derek Watts, etc). The core teams don't change between Dragon Age Origins to DA2 to DA3 or ME to ME2 to ME3 (unless someone quits or similar)."
We'll keep you posted if the team ever offers anything a little more substantial.