The paper scissor rock idea would be pointless. The idea of balancing is so that in a given game no matter who has what races both players should have an equal chance at winning. If two players chose random and both were evenly skilled, a large determiner in the outcome would be merely who got which race.

But anyways we know almost for sure there will not be a fourth race so all this doesn't matter. All we can do now is wonder what it might have been like.

...what about the possibilty of a new race in an expansion pack? Seems unlikely but I guess not out of the question.