Height balloon tests were conducted in Adventureland and one possiblity is that this could be a new Moana themed attraction. The rumor from Jim Hill is that Disney is revisiting the idea of a transforming coaster that was in development for an attraction based around the animated movie Atlantis. The original Atlantis attraction began as a standard coaster before converting to an inverted coaster in the middle of the ride.
With the announcement of the Tron attraction in Tomorrowland, it appears that this project is now dead.
July 20, 2017: On the latest episode of The Unofficial Guide's Disney Dish podcast, Jim Hill and Len Testa discussed that the Tron coaster coming to Tomorrowland likely means the end to this project in Adventureland.
April 24, 2017: WDWMagic.com user WDW1974 is reporting that the Fire Mountain/Moana attraction isn't happening in the Magic Kingdom because the ride would be deemed too intense.
April 24, 2017: OrlandoWeekly.com has posted an article that consolidated the Fire Mountain/Moana rumors as well as explain logistically where it could be located and how it might happen.
April 18, 2017: On a premium episode of the Unofficial Guide's Disney Dish Podcast with Jim Hill, Jim and Len discuss the height balloon test that was recently conducted in Adventureland. Jim suggested that the old transforming coaster idea called Fire Mountain is being considered with a Moana theme. Jim did specify that this was not guaranteed to be happening but it is being considered.
The attraction would likely have a long queue with the bulk of the attraction existing outside the main footprint of the park.
March 22, 2017: WDWMagic.com user lentesta posed the question about whether or not a height test took place recently in Adventureland.
August 10, 2003: JimHillMedia.com posts an article that references an Imagineering concept called Fire Mountain.