Interesting idea, though it makes it sound like the Underworld and Twilight movies then with the whole vampire versus werewolf feud. That sort of thing I wouldn't want to see in MK as it's been done enough elsewhere. I like how things were going with Nitara's MKA storyline with the story revolving around the Datusha. Given her story, it seems the vampires want to be left in peace but this could be a false pretence.
I have mentioned before that I wouldn't midn seeing the vampires become a threat. My idea was that they'd start selecting certain warriors to run into vampires. These would be the more acomplished warriors so as to serve as fighters to help protect their realm. Or, they could do this to create an army to beginning invading other realms or even just to enact chaos around Outworld and take revenge on Shao Kahn. Heck, they could even just want to go and tear Outworld apart by smashing the rest of the Portal Spheres and freeing more relams which then gives us options for new realms and characters.
Your version of the Animaility as a power up reminds me of the Neijin in MKDA. I don't mind a power up as such but to see the player transform mid match would to some seem like a blatent copy of the Bloody Roar series. Again, that's something I would not want to see. I'm not sure if you mean Nightwolf would keep his wolf form and fight on as one. Either way, I would not want to see that happen in game. An idea would be just to bring back the Neijin perhaps, and as Nitara or Nightwolf perform it (and this would apply to Nightwolf more), we could see a shadow of his chi in the form of a wolf. It could emanate from his body and show that he's just focused his power.

this idea sounds like a mash up of underworld and twilight thrown into an MK game lol. i don't like the power up idea at all. i rather Nightwolf be able to transform at least for a fatality/animality. i kind of like the idea of the vampires being a threat but if they are going to be a threat than why not make them a threat to more than just earthrealm? in anycase,this idea is not that bad but its not going to be anything close to MK9. MK9 will either follow MK:A more than likely...hopefully it wont be a reboot but that is possible too. maybe this idea can be something to ponder in the future.