Just to warn you about the movie, it may make you cry (from what I've heard about the director's previous works), and it may uncomfortable to people who aren't into feet.
I actually have no idea. I found it on tumblr and fell in love with the animation and how sharp and clean it is. If that's what it's from, then I may just have to see it for its beautiful animation.
It would certainly be interesting if they did, however, they've had four generations since Dark types were introduced to do that. I could see the Ekans line being more Dark-type than Rattata's though.
Do you think the Ekans line and Raticate should gain a Dark typing, to increase the presence of Dark types in Gen 1, back in Gen 2 when they gave the Magnemite line a Steel typing?