User blog comment:James12708/Possibility of a Mass Effect 4/@comment-2250460-20121028163027/@comment-24174486-20121028214314

"depending on your choices they made it that say if you let the Rachni live but Wreav is clan leader and Eve is dead that he goes to war with the Rachni again."

There already is a difference in the future of the krogan based on who is leading them. Merely because it isn't reiterated at the very end of the game doesn't mean that every outcome is the same.

"But if you had the right amount of choices the races were able to come up with a solution themselves without sacrificing humanity."

I'm sure that an idea like this is what they wanted to avoid through the EMS system. Mass Effect is about your choices having consequence—you shaping the face of the galaxy. An ending in which the player had to have made specific choices in order to get the best option would go against the style of the Mass Effect series. The final decision rewards the player for having made good choices and efforts throughout the series, rather than penalizing them for having made specific "wrong" choices.