According to Serebii the host of Pokemon Sunday said she loves electric types and with that would love to voice Zekrom. This post was then removed from her blog minutes afterward.
I think she knows it's part electric, but she hurried up and removed it, because she remembered that no one is supposed to know.
After reading that, I wondered if this is the location where Zekrom may be found.
It's a possibility. It could just be a random cave, but I think there's a chance Zekrom's location is here. Zekrom has some blue in his design, and the electricity in this picture is blue. He also seems to have a robotic look. Robots are electronic. It makes sense for him to be part electric.
If Zekrom was Electric/Dragon then Reshiram would be Fire/Dragon wouldn't he? It makes sense. Here is why:
Reshiram has a possibility of being part fire seeing as there is a torch for its tail. Maybe it controls volcanoes or actual fire.
The reasons why the legendaries for Black and White could be fire and electric:
Fire--you light a candle to see in the dark. It's light in darkness.
Electricity--you turn on a lamp when it's dark. It's also light in darkness.
Therefore, Fire and Electricity tie into the light/dark aspect. Both create light when there is darkness. It doesn't have to be so literal and be part light and part dark types. The legendaries could be part fire and part electric and still convey the same message. The titles make sense, because Black represents dark and white represents light.
Also, with fire and electricity, not only can they bring light, they can cause darkness as well. If you use too much electricity, it causes power outages (like the one in Sunyshore). Without power, you're in darkness. Fire also creates smoke. You can't see when there is smoke and ash. Therefore, there is darkness.
Fire and electricity control light and dark. Therefore everything I've said makes sense for the legendaries to be part fire and electric.
It's possible that the evil organization(s) in this game are looking to harness the legendary powers for their own advantage. It could be a battle between light and darkness using fire and electricity.
That's probably why the protagonists are older. 10 year olds shouldn't be messing with fire or electricity. It also explains the boots and the shoes they are wearing. Hiun city is an industrial city that uses a lot of electricity and fire.
Dragon/Fire and Dragon/Electric legendaries seem very possible for Black and White. According to wikipedia, "lightning can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge."
This is a combination of fire and electricity taking place at the same time. Light is the electricity. Darkness is from the smoke caused by the fire. Notice the colors? (White and Black.)
If you place the Pokemon onto the background, it seems like a very plausible idea.
This is from the main page:
"Reshiram's name comes from "shiro," which means "white" in Japanese, whereas Zekrom's comes from "kuro," which means "black." But as it turns out, the names also originate from the Japanese words "shiramu" and "kuromu," which mean "to grow light" and "to grow dark." Specifically, these words are used to refer to the sky becoming light and dark. Like we pointed out a few weeks ago, "hiun" in Hiun City's name can mean "clouds being blown by the wind." In addition to this, the bridge connected to Hiun City is named "Sky Arrow Bridge." So, we obviously have a sky theme going on in these two games in addition to the possible lightening or darkening of it.
What do these tidbits and the names of the Legendary Pokemon tell us about Black and White's plot? This is just speculation, but perhaps the games will involve a story related to making the sky night or day, similar to the whole land and ocean dichotomy in Ruby and Sapphire.
On the main page it was also theorized that Zekrom's tail could be a night generator.
This makes the Electric/Dragon and Fire/Dragon theory even more realistic because there is a sky theme going on already, and Fire and Electricity can each cause light, darkness, and problems with the sky.
If you are thinking that their colors do not match their potential typing, Reshiram has red highlights and Zekrom has blue highlights. I also noticed Zekrom has red and yellow eyes (fire) while Reshiram has blue eyes (electricity), to balance out the colors for the whole yin-yang thing they've got going on.