That's an interesting theory. Yes, why did Yoko ask Kogoro to do such a simple case? Geez, I wonder...! Hm... This is kinda random, but in the Clash of the Red and Black Arc, when the fire broke out in the cinema, they were watching a Yoko movie. I believe... Yeah, now I wonder about Yoko...
And no, I doubt Sera is the Boss. And Akai? I don't think so either... The Boss believes Akai to be the Silver Bullet, so... But who knows? I don't.