Who said ME4 was going to be open world? There is a new sci-fi game in development that will be open world, but it is done by CDProjekt, not by Bioware.
If they make ME4 into an open world game or, even worse, a MMO, I will start a holy crusade against EA. They slaughtered KotoR, they threw away Neverwinter Nights, they made Dragon Age into story-based Skyrim - if they dare do something like this to my favorite franchise, Mass Effect, even the Maker will tremble before my wrath!