Prediction: Jax will be the final antagonist of the show
Not along ago after episode 7 aired, I made a prediction that the SOMA/brain scan theory is real, and the revelation of that will break Jax, since the others have all formed bonds that could help them through such a revelation while Jax has pushed everyone away. I'm still all in on that theory and expanding on it with a new prediction: Jax will be the antagonist of the finale and final big threat of the show.
Jax's whole motivation for acting the way he does is "we're all just a bunch of cartoon characters and nothing we do matters cuz none of this is real." So getting confirmation that he's right and none of them are in fact "real" would be the ultimate reinforcement of that nihilistic outlook. Combine that with Kinger's confirmation in episode 8 that anyone in the Circus can conjure stuff with the right focus and mindset, and it's the perfect storm of circumstances for Jax to become a threat to those around him. He might not be powerful enough to completely warp reality like Caine was, but Jax could more than make up for it with the sheer cruelty he's shown to be capable above. Especially since he'll have no reason to hold back since none of them are real. The sheer stress on his mind will probably push him to the edge of Abstraction even as he lashes out at everyone.
Of course, the other Players can also conjure stuff, which I predict is how they'll fight back against Jax and try to subdue him, since they'd be on a much more even playing field than they were against Caine. Predicting that they'll also try and get through to him, make it clear that despite everything Jax has done, they still don't want him to Abstract because no one deserves that.
As for the outcome, I see two possibilities. It could be a good (or at least bittetsweet) ending like the climax of Steven Universe Future where the support of everyone is enough to bring Jax back from the edge, prompting him to finally break down and admit how wrong he was for everything he's done. Alternatively, it could be a tragic ending like Simon in season three of Infinity Train where Jax refuses to change even if it destroys him, sending a harsh but true message that some people simply won't change no matter how much others try to help them.