Was just thinking there’s no way Shang Tsung is the main antagonist of the game and he’s a pre-order DLC character.
It’s definitely someone else and I’m hoping it’s Onaga.
Shang Tsung is likely the main aantagonist. From the og MK1 through MK11 Aftermath, Shang Tsung is the most influential villain in the series. He was the first MK boss. In the lore, he's been there since the first tournament. He was instrumental in Shao Kahn's whole invasion of Earth Realm. He didn't have much to do with Shinnok, but there's the Deadly Alliance. Without the Deadly Alliance, there was no reason for Onaga to return, which set in motion the events for Deception and Armageddon. Then we find out in MK11 that Shang Tsung's whole purpose was to steal souls to power the crown that he created for Kronika. Because of this, he was the only one who could successfully weild the crown to defeat Kronika. He'd been working alongside her the whole time.
So, he's like the sole main villain left in MK because unlike the other villains, Liu Kang allowed Shang Tsung to kill Kronika.
In this new game, I think Shang Tsung will assemble his own team of minions, which could include Shinnok, Onaga, Shao Kahn etc, because it looks like in this new universe that Shang Tsung is the only villain powerful enough to challenge Liu Kang. Wouldn't really be an MK1 without Shang Tsung as the main antagonist.
The only catch is that Shang Tsung will be playable. That said, he may have this crazy final form as a boss similar to what they did with Shinnok in MKX. It would be sick if Shang Tsung's final form is the Dragon King or something similar.