Well, I’ve been saying it for a while now, but the Hagemans have finally forced themselves into a situation where the game has been reduced to Cloud Kingdom or Bust. Unless if Chen miraculously escaped the same way Clouse did, I don’t think there’s any way to avoid using the Cloud Kingdom.
(Chen escaping the Cursed Realm doesn’t really make sense for a lot of reasons, especially considering that Clouse was alone for his entire journey from wherever-he-ended-up-in-Ninjago to Stiix. If he’d mentioned anything about wishes and Clouse wanted to or had the ability to bring Chen along, Chen would want to come along. Clouse probably didn’t want to, for one thing. He and Chen are almost perfect mirrors of Skales and Slithraa back in S1: Clouse knows he’s better than Chen and wishes to dispose of him when he can. Considering that Clouse has magical capabilities far beyond anything Chen is capable of (if he’s capable of anything at all), he was probably able to easily escape the Cursed Realm, and left Chen behind. Chen doesn’t have the ability to escape by himself; my guess is that he and Garmadon both drowned inside the Preeminent. If Chen returns, the Cloud Kingdom will have to be involved.)
As for Pythor, the story is more... complicated. It’s difficult to say exactly what angle they’ll take here. However, as far as I’m concerned, it doesn’t make sense for Pythor to willingly turn against the Ninja again. After Chen’s deception was revealed and Pythor was honored by Arcturus, the all-time greatest general of the Anacondrai tribe, I think he’s going to stay good for a long time. The only question in this case is, for one, whether he’s being bribed somehow (because if someone had a good enough incentive, Pythor would probably take it - I can’t think of a good incentive, though, honestly), or if he somehow died offscreen between the end of S4 and now.
Ultimately, there are just a lot of things that we don’t know at this point. And it’s hard to tell what his role will be, without any actual pictures of the set he supposedly appears in.