huh? Double sided/transform planeswalkers wouldn't change the number of planeswalker cards. It's gonna be 36 planeswalker cards in the set, not 36 different characters. If one card has two different planeswalkers on it, that's still just one card. In fact, I think it's more likely we get multiple versions of the same planeswalkers. i.e. 2 jaces, 2 lillys, etc.. Potentially a cycle of them, one version before the war starts, one version during/after the war.
Plus, the teaser trailer was showing like, what, 18 planeswalkers I think? If there's just 2 versions of each of them, that math would line up well.