Honestly MK12 is going to be very interesting. After the Great Kung Lao appearing in the good ending of MK 11, it sets up the next installment taking place during his time before the 1st game so I can see some old faces really making huge comebacks;

1. Kai- like Liu Kang and the Kung Lao we know, Kai can really play a major role as the other half of the Shaolin Monk duo by instead of existing in the future, being introduced in this time period .

2. Nitara- Killer Instinct really did a good job with Mira as a vampire character. Vaeternus really needs representation and if done right with a killer new look, Nitara could be amazing.

3. Hotaru- He is the ultimate warrior of Order. If Onaga happens to be the main villain, Hotaru is a given to bring back.

4. Havik- as the Cleric of Chaos, Havik- has been alluded to for too long and he should return to shake things up. Plus, it would be awesome to see a rivalry between him and Hotaru.

5. Quan Chi- I can see a younger more primal Necromancer demon version of Quan appearing. I'd assume he would be more powerful as well.

6. Li Mei- she would serve as one of Outworld's champions even if it was by force. Onaga could hold something over her head to ensure her participation.

7. Ashrah- she could serve as one of Quan Chi's henchmen or as an enforcer for the ruler of Nether Realm.

8. Onaga- the Dragon King and Protector/Emperor of Outworld. Would like to see him with a humanoid look with the gray scaly skin with the cape on his armor being his wings in disguise

Storywise, it would be interesting to see the story revolve around Onaga's rule of Outworld and his ambition to take over the realms.

Liu Kang would be the one to petition the Elder Gods to establish the Mortal Kombat tournament which halts the Dragon King's plans.

All the realms introduced up to this point would be represented in the tournament along with a few new ones and we could see their Protectors in the story.

So Earthrealm- Liu Kang, Outworld- Onaga by default, Chaosrealm- Havik, Seido (Orderrealm) Selene, Netherrealm- possibly an Oni Sect that involves Quan Chi, Vaeternus- Belok could be their protector and was an unused fighter from MK4, Edenia- Argus and Delia, Arnyak- a Kytinn cleric

New realms ideas....Cybronia- a techno realm that the future Lin Kuei exploits for their advanced technology used in the Cyber Initiative. Obsidian would be the realms protector and we could see new cyborg characters that have similar abilities to Cyrax, Sektor and robo Smoke. Vector and Rex would be the new Sektor and Cyrax.

Zaterra with Khameleon as it's protector and would set the stage for Reptile or another of his species be introduced.

The realm of Prague- realm of the undead so would could maybe have a zombie fighter....Havik doesn't count as a zombie fighter imo.

I'd really like to see a good sorcerer character introduced that could offset Quan Chi. A character similar to Kan-Ra from KI, and Anankaris from Darkstalkers in terms of look and powers and I would name him Raza.

These are just some of my ideas

Somewhere down the line this could justify a reason for the emergence of Khrome, the one they all detest. I say no new characters apart from the magnetized liquid metal one, taking into consideration each and every we know in MK (officially). Not sure 'Cybronia' would be the dwelling place of the character, although it would make perfect sense.

Aside from a certain user overpromoting Khrome in a trolling fashion, iirc the only real obstacle was the name already being used by an existing copyrighted character.

Kurial, Merc Fury, Kobalt, Kaast, Kwixil/Kwyxyl, Xilvr, Talik, Mrohk, Kinja, K'Netyx, Kinetikore

Ka-Tra

Taven could feasibly appear at some point in the future. He was removed from the cave by Kenshi and Takeda in Takeda's MKX ending, and then they went out to get their revenge on Daegon. It could be possible that the reason Takeda doesn't appear in MK11 is due to him and Kenshi going through their endings stuff at the time the MK11 story takes place.