Can't kill franchise favorites. No one liked when they took Sonya and Kano out of MK2. No one liked removal of Scorpion, Reptile, Mileena, Cage, Raiden, Baraka from MK3. No one liked removal of Kitana, Mileena, Baraka from MK4. You just don't do it because it's not good for business. MK9 was successful because the reboot went back to what old fans enjoyed. Most Arcade heads stopped messing with MK after MK4, and have almost no clue who the 3d MK cast is. The new cast also have weirdo designs because Tobias didn't make them.
My guess is that we will get most of the old cast from MK9 after you rescue them/unlock them from the Netherrealm, but some will stay in there until the next game. From there we will get close to 15 new characters including DLC. Honestly, if NRS was somehow able to convince WB and the Wachowskis to let them put agent Smith in the game that would be incredible. I doubt WB will ever let them fatality Neo, but they might be able to compromise on agent Smith, either that or another horror character (Jason being the logical successor to Freddy).
40+ characters will be the roster(Similar to Ultra SF).
You can logically conclude that they will not have a roster that's considerably less than Ultra because it would look flimsy by comparison, but they won't fill the 40 with 3d characters. Not going to happen. The Who's next teaser is a red herring to make you think the dead characters will stay dead.
I'm most excited to see if they put in totally new characters.
