Rule book seems extremely clear and well thought out. We have a million questions about Dune still, despite two designer Q&A's and years to figure this stuff out, but I have only come across one question so far for Rex (and it's probably something I'm just overlooking because it was covered in Dune):
1. When exactly do the Xxcha make their prediction?
The faction sheet says "during set-up," and while set up is very quick (thank you, traitor cards!), it involves several steps, each of which after determination of factions could significantly affect the Xxcha's decision. In Dune, the Bene Gesserit made the prediction before traitors were drawn, which is how I'll play it until official word or someone points it out in the rules to me, but given the many nuances to Rex, I don't feel comfortable assuming it is supposed to be like Dune.
I do have my doubts though since in token set-up the rules mention if players have decisions to make, they make decisions in turn order. It could be (fingers crossed) just a failsafe in case they decide to expand the game, as the only player with token set-up decisions in Rex (and indeed the only example given) is the Sol player. But it could be they meant the Xxcha to decide their prediction at any time during set-up, which would give them a tiny bit extra info to work with if they happen to be seated after the Sol. But it isn't a token set-up decision, so I don't think it could be argued definitively that that was the intention.
I am partial to the Dune timing because I believe the player should have to work at making the prediction come true rather than just trying to read the signs as best as he can and make an educated guess. Not a big deal either way as the traitor draw isn't a huge help to making a prediction, and Sol set-up I don't see as much an advantage at all. Still would be nice to know for certain though.
Feel free to post other rules questions here. And we can probably answer most questions for each other, but if not, maybe it'll get an FAQ.