I definitely agree with harrisonpink. Have you seen Jim Henson's Storyteller? They use a lot of Russian folklore and they all seem like that.
As to the mythology, I think that so much of the charm of the KQ games was the hidden (or not-so-hidden) references to folk-tale and mythology, but also to earlier games in the series and other Sierra games. I think it would be great to keep that going, possibly including references to other TellTale franchises.
Don't forget North American folklore like Paul Bunyan, or the stories of Washington Irving. Or bigfoot. For those of us who remember the good ol' days of computer adventure gaming, how 'bout references to some classics, like Death on the Caribbean, The Great Underground Empire, Below the Root, or even Michael Crichton's Amazon.
I guess I'm the only one who would think that including references to LOTR would be a good idea. These reimagined KQ games must appeal to OG fans of the series as well as new, younger gamers. Besides, these references don't even need to be part of the puzzles, just background.
Regarding Asian folklore, I think this would be very appropriate to the series. I think KQ was always willing to explore myths that would be recognized by its audience, regardless of origin. I recall learning some Japanese folklore when I was very young, like Urashima Taro. And who among people my age doesn't remember Liang and the Magic Paint Brush from Reading Rainbow? Or Tiki Tiki Tembo? Or the *ahem* Five Chinese Brothers. I think there's definitely room to include true folklore or fairy tales from many other cultures. One of the funnest things about playing the original (especially 1-4) games, was going to the encyclopedia or library to look up the source stories or myths for inspiration to solve the puzzles. Living in such a small, small world as we do today, I think mixing the familiar with the exotic would keep that sense of excitement, as well as opening the franchise to more people.
One last thing. I too, really loved the works of Lloyd Alexander. So I would definitely recommend reading the Mabinogion, (which, I believe is the greatest inspiration for the Prydain Chronicles).