I think we kind of went through this already when the trailer/preliminary cast pictures came out.
I think the best way to describe the situation is that although the "atmosphere" of the world of Avatar is "orient/inuit/japanese/chinese/etc-inspired" the show is more or less equivalent to
Mukokuseki. I recall someone showing off a few pictures from some overviews of "extras" from the Earth Kingdom and Water Tribe "military" encampment and the Air Nomads; these nations aren't "wholely, universely, one realistic ethnicity". Here are two good arguments concerning said pictures:
A and the followup by Ninjajack,
B
Honestly, what good is a "petition," "boycott," or "riot" now if the movie is already being filmed and the casting is DONE. I highly doubt they'll start firing cast members left and right, half-way through production, with a good amount of budget spent, due to "internet protests." I can honestly understand it is a little off from what a good number of people expected, and that the "racial discrimination" in Hollywood is a potent issue, but such is the way of the "live-action adaption;" things, especially for animation derived works, doesn't always translate to reality exactly how it was in the original.
At any rate, "raging against the creators/Shyamalan" when we only we have a few pictures, scraps of information, and rumors (that should always be taken with huge amounts of salt) and still haven't a finished product to validly target it against, kind of takes the wind out of the sails of these sort of things. As it has been said countless times before, reserve your anger and complaints until there is actually something substantial to release said rage at, such as the actual fully released movie.
For all we know, despite a few descrepencies, it might actually be...good.