The area behind Asia has looked basically like that since the park was built. They seem to use it for storage and staging for other projects. There is nothing in the Google Maps that would lead me to believe they are going to build there any time soon.
All indications are that it is going in the CMM area.
There was a picture recently over at Orlando Theme Parks News showing a survey marker in the CMM area. Can't say for sure it is for Avatar, but it's an interesting sign.
Evidence of actual construction, no matter where they build it, will likely surface first as a permit to the South Florida Water Management District. This would proceed construction by at least a month or two.