Skarlet, Mileena, and Ermac because something bound to have changed them completely over Shao Khan's death + Fan service
Smoke because of that Kotal Khan variation picture
Quan-Chi because story.
This is why I highly doubt its 8 because of the high chance of Liu Kang being in the game.
Skarlet really isn't even a character yet because, firstly, she was just some background ninja and then became DLC that didn't impact the story, so maybe she could be counted as a "new" character, but still retain what had already happened with her in MK9?