What I'm predicting....

Returning:
1. Raiden
2. Kano
3. Scorpion
4. Sub-Zero
5. Quan Chi
6. Liu Kang
7. Tanya
8. Sareena
9. Kenshi (boot #2)
10. Mileena
11. Baraka
12. Reiko
13. Johnny Cage
14. Cyrax
15. Fujin (boot #3)

New:
16. Cassie Cage
17. Ferra Torr
18. Kotal Kahn
19. D'Vorah
20. New Shokan (A female Tiger-type shokan, boot #4)
21. New Cyborg (A female Cyborg!)
22. New Shaolin Monk (a descendant/student of Kung Lao)
23. New Black Dragon Member (TREMOR! boot #5)
24. New Raptor (Son of Reptile and Kahmeleon)

Unplayable Boss:
Shinnok (Boot #6)

DLC:
25. Goro
26. Ermac
27. Li Mei
28. Havik
29. Rain
30. Sonya Blade

Guests:
31. Jago, Orchid or Fulgore (Killer Instinct)
32. Michael Meyers

We've got 24 spots on the select screen, plus DLC and guests, so I think that 32 sounds like a very plausible number, considering that the last game had 34...not counting Shao Kahn, Goro and Kintaro.

Sub-Zero
Scorpion
Raiden
Kano
Quan Chi

Kenshi (given)
Fujin
Tanya
Sareena
Frost
Shinnok (given)
Bo Rai Cho
Havik
Tremor

Starting roster: Scorpion, Sub-Zero, Raiden, Kano, Liu kang, Reptile, Shinnok, Kenshi, Quan Chi, Tanya or Mileena, console exclsive character and 12 new characters
DLC : 1: Goro, 2: New character, 3: Ermac, 4: Havik, 5: guest character,
6: Termor (techinally, a new character)

36 Characters
3 x Rows of 12

my MKX roster prediction list:

MK9 returning

1. Scorpion
2. Sub Zero
3. Raiden
4. Quan Chi
5. Johnny Cage
6. Reptile
7. Milenia
8. Baraka
9. Kano
10. Ermac
11. Kenshi
12. Rain

MK4-MKA

13. Havik
14. Bo Rai Cho
15. Tanya
16. Fujin

NEW

17. Kotal Kahn
18. D'Vorah
19. Ferra/Torr
20. Cassie Cage
21. Female Medusa Character
22. Male Shape Shifter
23. Female Kung Lao Descendent
24. Male Demon

Unlockable

25. Kitana (Unlocked during Story mode)
26. Shinnok (Boss #1)
27. Liu Kang (Evil Boss #2)
28. Leatherface

DLC

29. Goro
30. Killer Instinct Character (Xbox One)
31. Kung Lao
32. Jax
33. Cyrax
34. Sector
35. Sareena/ Sindel/Frost
36. Shao Kahn

Returning:
1. Scorpion
2. Sub-Zero
3. Raiden
4. Kano
5. Quan Chi
6. Kenshi (Boot #2)
7. Fujin (Boot #3)
8. Reiko
9. Tanya
10. Shinnok (Boot#6)
11. Johnny Cage
12. Reptile
13. Mileena
14. Sektor
15. Cyrax

New:
16. Cassie Cage
17. Ferra Torr
18. Kotal Kahn
19. D'Vorah
20. New Outworld Female (Boot#4)
21. New Black Dragon (Boot#5)
22. New Human Female
23. New Male
24. New Male

Unplayable Boss:
Quin Chi: Sub-Boss


DLC:
25. Goro
26. Ermac
27. Sareena
28. Havik
29. Nitara
30. Liu Kang

Guests:
31. Fulgore (XBONE)
32. Sweet Tooth (PS4)
33. Predator

Bravo.

Im saying there is 24 and 6 DLC characters.

MK9

1. Scorpion
2.Sub-Zero (Bi-Han)
3. Raiden
4. Kano
5. Quan Chi
6. Kenshi
7. Mileena
8. Ermac

MK4-MK7

1. Shinnok
2. Tanya
3. Fujin
4. Li Mei
5. Bo Rai Cho
6. Havik
7. Hotaru
8. Frost

New

1. D'Vorah
2. Cassie Cage
3. Kotal Kahn
4. Ferra/Torr
5. Tremor
6. Forest Fox
7. Guest Character PS4/XBONE Exclusives.
8. ???

DLC

1. Goro/ Kintaro(as a skin)
2. Kitana
3. Reptile
4. Smoke
5. Reiko
6. Ashrah or Sareena

I'm guessing off the bat, initial roster. 15 new 15 classic

Classics
1. Scorpion
2. Sub-Zero
3. Raiden
4. Kano
5. Quan Chi
6. Shinnok
7. Reptile
8. Johnny Cage
9. Ermac
10. Kenshi
11. Fujin
12. Tanya
13. Bo' Rai Cho
14. Liu Kang
15. Kai

New
1. Terra Forr
2. D'vorra
3. Kotal Kahn
4. Cassie Cage

And I have no idea after that.