@In Exile: Just to throw this out there but if they announce MP it does NOT mean it has heavy overlap with SP and it does not mean new mechanics. It just means it has MP. You, personally, would 'assume' those 2 things but the inclusion does not mean that. I would 'hope' that it has no tie with the SP, other then maybe in theme or 'reason' for the MP stuff to be happening. Such as are characters having ties with the inquisition but not actually effecting SP.
As for the whole new mechanics, outside of PvP obviously needing something it would more likely mean mechanics present in SP not being there in MP. For instance tactical camera and pausing would more then likely not exist in MP. MP would not magically make those disappear from the SP component. Personally I'd love it if they just used the overmaps for SP and just deactivated all the quests for a MP-Free roam mode. Not all of the areas just the 8-10 large maps with dungeon's to explore with buddies. We could each have our own mounts, stuff like that.
If it exist I expect something closer to ME3 but it would be nice to get something grander. Hell I'd be happy with a 2 player co-op allowed in the story. Having a friend come into my SP game and take up 1 of the spots in the party but everything else stays as is, Tactical cam, pause/play, using team members and all that. And before anyone whines about that idea, it existed in their original games, BG, BG2 and NWN all had that. They haven't done it since cause they felt it would be boring to watch people have conversations as the 2nd person, but they have mechanics now that let you do conversations with out that whole view and, frankly, I'm willing to sit around while my buddy has those conversations if It means I get to tank for him in his game.