I was thinking that maybe the next game could be a huge Dark Holy War between Dark Raiden and Liu Kang/Kitana. They would appear to be the main threat but the real threat would be the One Being and his own forces that he enslaves. Here is an idea for the premise of the story;

Shinnok has been neutralized. His severed tossed at the feet of the Netherealms new leaders as a show of his power. Dark Raiden warns Liu Kang and Kitana that no one would stand in his way, that all threats would be destroyed. That was several years before it happened. In a blink of an eye all the realms were attacked triggering the deadliest Holy War since the war between the gods and Shinnok. As war between Raiden and the Netherealm intensified, the real threat was gaining strength from the shadows. Once he is at full strength and his army is complete, all the realms will be devoured by the One Being......Olympus.