Reportedly there are expansion plots adjacent to Pandora: The World of AVATAR that can be used for a new attraction and a table service restaurant. The only public source on this information indicates the existing of the expansion spots, not that anything is currently in development.
January 21, 2020: WDWMagic.com user WDW Pro is reporting that Disney is considering an expansion to Pandora: The World of AVATAR ahead of the new movies coming out alongside the sequels.
The expansion would likely be into the cast member parking lot area and would likely be a high capacity indoor attraction.
Any expansion would be in competition for budgets with a Star Wars: Galaxy’s Edge expansion and reportedly no decision has been made.
August 22, 2019: WDWNT.com is reporting that a yet to be determined E-ticket attraction has been approved for Disney’s Animal Kingdom with an opening date of 2024.
February 21, 2019: WDWMagic.com user marni1971 is suggesting that an expansion to Pandora would take place before an expansion to Star Wars: Galaxy’s Edge.
June 11, 2018: On Episode 166 of the Disney Dish Podcast, Jim Hill discusses the idea that the 3rd attraction coming to Pandora: The World of AVATAR would largely play on events/visuals from the 2nd and 3rd Avatar movies.
October 30, 2017: WDWMagic.com user marni1971 is reporting that an expansion to Pandora is fueled by the land not having the operational capacity originally anticipated.
July 14, 2017: Vulture.com is reporting that Pandora: The World of AVATAR has two expansion plots that could be used for an attraction and a table service restaurant in the future.