This will be Ermac's most important role in the story ever, more so than even MKD. I'm very much excite. I can't wait to see how the souls battle for supremacy inside Ermac's body over 25 years.
My guess is that, in the beginning, we will see a very fickle Ermac whose souls are chaotic and violent. Inside his body, there will essentially be another Edenian war waged by Shao Kahn. Haha, side note... how fucking meta would it be if the souls inside Ermac made their own Mortal Kombat tournament within the body as a set of rules Shao Kahn must follow to overthrow the Edenian souls?
I think during the first 5 years, Shao Kahn will slowly gain control, making Ermac lean more towards evil. Towards the middle/end, the souls lead by King Jerrod will revolt eventually taking control. I'm not sure if anyone will aid Ermac in achieving "enlightenment," but if it is anyone, it'd likely be Kenshi or Scorpion. Scorpion and Ermac could probably help each other. Scorpion likely has a shred of honor or gratitude towards Kenshi for temporarily cleansing him, so if he is able to find a balance between Hanzo and Scoprion, he'd likely want to do the same for Ermac.