Over at the official Bioware forums, community manager Chris Priestly have revealed some details on the next game in the series, and how people needn't worry about how their choices will apply to the next title.
"To call the next game Mass Effect 4 or ME4 is doing it a disservice and seems to cause a lot of confusion here. We have already said that the Commander Shepard trilogy is over and that the next game will not feature him/her. That is the only detail you have on the game."
"I see people saying ‘well, they'll have to pick a canon ending'. No, because the game does not have to come after. Or before. Or off to the side. Or with characters you know. Or yaddayaddayadda."
"That doesn't mean that events of the first three games and the choices you made won't get recognised, but they likely won't be what this new story will focus on.
"What makes it Mass Effect is indeed the alien races, the technology, the lore, history, etc. You can safely expect those in the next Mass Effect."
Well, that's one way of actually revealing very little. The next Mass Effect is in development at Bioware Montreal and makes use of the Frostbite Engine. No release date has been confirmed.