^Out of curiosity, has it actually been attempted before? If so, I wasn't aware.
Regardless, I wouldn't really call this a serious attempt to make an otherwise singleplayer RPG multiplayer. It sounds more like an especially separate game that uses the main game's engine and assets. Probably the most apt comparison would be the relationship between the Half-Life games and the Team Fortress/Counter-Strike games.
What makes it unique is the "spending" of points earned from MP in the singleplayer campaign (still not crystal clear on how that'll work.) I suspect the rest of the "Galaxy at War" system will be for integrating things like facebook and mobile phone games.