Well Sub-Zero and Scorpion are confirmed. No use debating their participation in the game. Raiden and Liu Kang are two other guys I feel are pretty much locks. Liu Kang is the original protagonist, and really still is, in some ways. As Ed Boon apparently once said: The Luke Skywalker of Mortal Kombat.
I think the game may have two bosses, one from DC (Darkseid?) and another from Mortal Kombat (Shao Kahn, seeing as he is the most iconic main villain of Mortal Kombat). I doubt story is their first prerogative in this game, but given his soul pledge to Shao Kahn, you'd think Shang Tsung would be hanging around. This doesn't bother me, as I feel Tsung is iconic enough. He was the first villain of the Mortal Kombat games, and his morphing is something a lot of people remember. He was also the bad guy in the MK movie people choose to remember.
So that takes us up to five characters: Sub-Zero, Scorpion, Raiden, Liu Kang and Shang Tsung.
Throw in Sonya Blade and Kitana. I think we will get at least two MK ladies, and Sonya was the first female of MK, and she's a favourite of the MK Team. She'd also mesh up well against the DC Universe characters. Kitana is the classic masked female, and while Mileena may be cooler to some, I think Kitana is generally seen as the "primary assassin girl." Her fans being used as weapons make a good visual, too.
Now we're at seven characters: Sub-Zero, Scorpion, Raiden, Liu Kang, Shang Tsung, Sonya Blade and Kitana.
Goro is pretty synonymous with Mortal Kombat, I think. As a sub-boss, he was something completely different, and something that helped put MK on the map. He's since become somewhat of a staple of the series, being the only sub-boss to really return, and undergoing several personality changes. The Shokan Prince almost feels like a comic character. He'd make a great counterpart for Doomsday, too.
This leaves us with two spaces. I want to say Johnny Cage makes it in. As someone put it in his game card (I think it may have even been Ed Boon), he's the classic "comic relief" of the series. That makes him fairly iconic, I think. His character also played a big part in the MK movie, and Linden Ashby stole a lot of scenes. People would remember Johnny Cage from the classic games, the movie, and if you take into consideration he was almost literally going to be Jean-Claude Van Damme, JC was almost the first crossover involved in the Mortal Kombat universe.
With the last character, I can see it going many ways. Personally, my preference, for whatever reason, is to go with Kenshi. His telekinetic powers would set him apart, without being anything that needs too much explaining. He's got a cool look, and the sword stuff helps him avoid getting lost in the shuffle. Kenshi is probably the most unique character from later MK games.
Jax is a favourite of Ed Boon, and the metal arms thing isn't exactly commonplace. He could very easily make it in. You also have Kabal, who is a vigilante, which fits parallel to Batman, for example. He's also got a good look. Mileena, as I mentioned, would fit into this game very well. The only thing more iconic than Kitana and Mileena separately is Kitana and Mileena together. Baraka has the blades, which may not have been entirely original, but he stands out as a memorable character to a lot of people. It'll be the closest a lot of people will come to playing Wolverine and Batman against each other.
Reptile completes the ninja trilogy. He isn't exactly a background character within the series. And finally, I could see Sindel making it in, just because she would be a great counterpoint for Wonder Woman. Hell, the woman just runs her own realm, was the bride-to-be of the main villain of the games and was the key to the third story -- it's not like she's unimportant to the series.
I'm going to rule out Reptile and Mileena, just because they are too alike other characters. Jax is a favourite of Boon, but do we really need two of Earth's Special Forces? Maybe they feel like they need a token black guy, though? Kenshi may not be iconic enough, as much as I hate to say it. It's down to Kabal and Sindel, I believe. Both have styles to them that would fit a comic book, but I think Sindel gets knocked off because Kitana is hanging around, and Sindel dying gives Kitana a story worth a damn. The new grieving queen finds universes merging around her, and doesn't know what to do. Even though I'm not a big fan of him, I can see Kabal getting the nod, Hookswords and all. He sort of covers Kano's contribution to the original game (criminal), and he's got a unique look, some good special moves, and he's quite popular within the games.
So my final guest list is: Sub-Zero, Scorpion, Raiden, Liu Kang, Shang Tsung, Sonya Blade, Kitana, Johnny Cage, Goro and Kabal. The last slot I am still fairly unsure of.
