Note: All credit regarding this information leak goes to XOF.
Among these, are cards owned by the protagonist Jaden Yuki and other prominent characters such as Aster Phoenix, Chazz Princeton, Alexis Rhodes and Bastion Misawa, meaning that they might be the first unlockable characters once GX is added. The datamine also shows the rarity of some cards and how duelists could get them.
Zane is a powerful duelist from GX series, his deck is themed around Cyber Dragon and it's other forms and fusions, his deck then centered around both Cyber Dragon and Cyberdark later on in the series.
For one, just because it was used in the manga doesn't make it a major card. Axel uses it, but, assuming he gets added, it's not like Electro's gonna get an animation, and he won't be a level up reward. I doubt Electro will even get a voice clip.