But, James has also made it very clear that the main premise of Avatar 2 was expanding and showing more of Pandora, the parts that didn't exist in the original movie. As the themed area & the movie were developed in conjunction I wouldn't be surprised that a lot of avatar 2 is in the land. Remember Avatar doesn't have a very good plot, that's not why it exists, it exists for Pandora.
That being said, I don't think Disney will allow the themed land to be delayed. The development stage is out and I don't think Cameron or his producer have any involvment in the current stage. I wouldn't be surprised, however, if James tries to get it delayed