Quan Chi's plan seems to be something developed in thousands and thousands of years. That's how he double crossed Shinnok.
Besides, Shinnok is arrogant. He thinks as an Elder God. IMO, he shows half trust on Quan Chi and half arrogance, thinking a creature like the oni would never get powerful enough to overthrow him.
I can't see Quan Chi not having a big role now. In the past, he had Scorpion and The Amulet. The he had the mummified army of the Dragon King.
Now, he has Scorpion, at the least for a while, The Amulet, revenant of the best warriors of Earth and Outworld (considering Edenia was not emancipated), and we don't know if any Dragon King's army will be introduced, and far from that, we don't know what is THAT THING ON HIS CHEST.
The sorcerer is way more dangerous this time. Quan Chi seems to leave the "advisor" role to a general, and this before any ancient ruins discovery. A boss...well, bosses we face as the last one. If he will be one to beat as a boss, I don't know, but he is rocking even before the game.