You know the typings have to do with the atmosphere, right? From the beginning I've heard rumors of a connection to the sky, no, atmosphere. Team Plasma would fit right in because it is a super-heated soup of ionic particles. Zekrom is Dragon/Electric, symbolizing low pressure/sinking air/lower atmosphere, and Reshiram is Dragon/Fire, symbolizing high pressure/rising air/upper atmosphere. The activity of the atmosphere acts like the teardrop parts of a Yin-Yang symbol, constantly spinning.
Maybe the rumored Dragon/Ice type symbolizes the outermost layer of the atmosphere, which is freezing...
How come no one has noticed the sky theme rumors... Hiun City's name (bad luck/cloudblown winds), the windmills, sky arrow bridge, the airport... Oh yes and I saw the idea of a sky theme as possibility on Pokebeach when one of the very first scans was revealed.