It's been pointed out, while watching some of the story mode trailers, Current/Older Jax appears to have joined Kronika's cause. This is mostly due to the attire he was in and him at odds with Jacqui and Younger Jax in the Old School New School trailer. After this was pointed out and discussed, people where trying to figure out why Jax would have done so. There have been some theories.

1) Jax (sometime between MKX and MK 11) has died and Kronika resurrected him or plucked him from the timeline before he died. <--- this one makes a little more sense than the next one... especially since Jax died in not one but multiple endings in MKX. All at the hands of Erron Black. So this could infact be one of the few arcade endings that are made canon.

2) Older Jax, in the new Kronika Uniform, was seen to have normal arms again. So some have said that it was simply a case of Kronika giving Jax back his normal arms. I don't agree here... Jax doesn't strike me as that shallow...that such an act (especially when he does indeed have fully functional bionic arms) would get him to turn on his friends/Allies.. especially Sonya who is opposition of Kronika and Co. I don't think it'd be something like that to get him to change sides.

On to my personal theory on the matter. I believe it has to do with Sonya herself. It's been made known (through accidental slipping of an intro between Cassie and Raiden) that Sonya is going to die in this game. It was later said that this "death" was going to apparently take place in the very first chapter. So right in the very beginning (Which..side note... if this death turns out to be permanent and not "fixed" by the end of story... I may have to kill someone. Just sayin').

What if Kronika promised to bring Sonya back, if Jax agreed to help her side win? This I could see happening. This I can see being important enough for Jax to turn on his friends/allies (quite possibly the only thing..excepting, of course, Jacqui). Jax considers Sonya family and loves her a lot. If Kronika made this offer, I could definitely see Jax taking it. Sonya is that important to him.

Do any of you have a theory on this? Or even thought on it at all? I've been thinking hard on it because Jax is, in my impression, a very loyal character. It would have to take something big for him to switch up sides and help people who are enemies of his allies. What do you all think? Are you more in line with either of the top two theories mentioned? Or do you have one of your own? Please share. These are opinions and we don't know what's up in story yet so.. no one is wrong. It's just thoughts.