I agree with you 100% on that having Sird be a part of Plasma would be WAY too much. But how can there be two separate evil forces in one chapter? Name one time in Pokemon Special that that ever happened. It remains doubtful that BW2 will even be a long chapter. There's always a central plot in one chapter so having two major separate forces wouldn't work out.
I'm not so sure about that. Don't forget that BW2 aren't remakes or like the 3rd games of a generation, they are sequels. There is a possibility that the BW2 arc is longer than you think. Even thought we won't see the beat all eight gymleaders in the arc, but I'm sure there will be a lot of traveling to introduce the new places. Hue wants revenge against team Plasma and I don't think he'll get it in three volumes.