Woo, another discussion about a WoT game!
Regarding setting, I am not too much of a fan of the concept of the main setting being a mirror-world. Not in an "it would disinterest me", way, it's just that depending on the points of divergence... well, it's not the same world that I read and fell in love with!
There are definitely ways to have a fun game without having to play through the Dragon Reborn stuff, though. Setting the game several centuries earlier (but definitely post-Hawkwing), would give similar nations and cultures to the game, but without big canon events looming. Easier to have a PC Amyrlin, Queen of Andor, and monarch of Cairhien, and all that. And there's a lot room for the game to go ahead without being bound by canon conflicts.
Then there is the post-book setting, which I think could be pretty nice -- with the Last Battle over, there's a whole new Age of possibilities! And with Asha'man and female Warders being a lot more viable as concepts, too. But the drawbacks would be that it could be spoileriffic for both newcomers from the Amazon show, and those who dropped off from the books halfway through. And besides, a Fourth Era game may even seem somewhat alien -- the all-female Aes Sedai is part of the series' charms, in a way.
I would definitely enjoy a game set during the books, too... but things would get messy once the big, canon changes start happening. A post-Aiel war game would work nicely though, in my opinion.
As for political stuff, two zones would work nicely (Tar Valon and Cairhien/Andor) with a largely Aes Sedai/Warder population in the former, largely non-magic in the other. I don't think domains should necessarily be completely Arxian, though.
As for rare concepts, there are gleemen, Blademasters, wolfbrothers, Ogier... all of which could be super interesting.
I would also think it makes sense to have PC Black Ajah. The scale of them is very large in the books, and some joined just for political influence rather than for the evulz. I am not sure about male channelers outside of metaplots in the case that saidin is tainted in this setting, however.