The only rumor I've heard is that Disney has grown shy of animal attractions, because of either real or expected protests since they're "profiting" off of animals. Otherwise, Indiana Jones is expected to go into DAK where Dinoland currently is.
I personally don't think they should be adding any new continental zones until Asia is given a proper shake. I expected some of the Himalayan terai animals to come in when Expedition Everest opened, and at least an orangutan when The Jungle Book came out. Neither happened of course. Instead we got dumb blue cat people.
I've not heard anything regarding the rumor that Disney has grown shy of animal attractions. There were protests regarding Disney's animal attractions around Animal Kingdom's opening, but I've not heard much about any sustained protests since (if Disney had been scared off by the initial protests, I'm not sure the company would have gone ahead and added Asia afterwards, as until the much later addition of Expedition Everest, Asia (like Africa still is) was mostly centered around the animals).
There has been a persistent rumor that what is currently DinoLand USA could give way to an Indiana Jones area, possibly centered on South America. Most of this rumor is probably attributable to the (relative) ease with which Disney could replicate its Disneyland Indiana Jones attraction over Dinosaur (which is constructed on a very similar blueprint). I have seen no particular speculation or sourced rumors that any such Indiana Jones/South American area might include new animal attractions. The most recent word on this is that any large-scale retheme has been scaled back, thus leaving DinoLand, but replacing the current Chester and Hester's Dinorama and its attractions with a roller coaster of some kind (presumably the Dinosaur and Boneyard attractions would remain).
All this having been said, I think Disney is unlikely to add any significant new animal attractions in the near future, for several reasons. First, the park has been recently expanded with the addition of Pandora and the expansion of evening operating hours with several new entertainment options; this has helped temper the once-widespread notion that Animal Kingdom was a "half-day" park. There is enough to do at Animal Kingdom for most people, and with the Dinorama area arguably the only area in the park that needs substantial work, I would not foresee huge future investment in the foreseeable future. The addition of Pandora, River of Light, the after-dark version of Kilimanjaro Safaris, Tree of Life Awakenings, and other entertainment options quite substantially improved Animal Kingdom, so I would not anticipate anything large going in. Second, Disney has announced many future attractions and other plans for its other three parks; in particular, both Epcot and Hollywood Studios in the midst of major redevelopment (Hollywood Studios will be mostly complete when Star Wars land opens in late 2019; Epcot has just begun several large construction projects, and a significant redevelopment of the Future World area has been announced), with several additions to the Magic Kingdom as well. These announced new attractions ought to keep Disney busy up to (and perhaps past) the upcoming 50th anniversary of Disney World Resort in 2021. Thirdly, I'm not sure that Disney or many of its guests (outside true zoo fanatics) see much need in increasing the number of animal attractions. Disney went out of its way to establish Animal Kingdom as more than a zoo, and the addition of substantial animal exhibits (outside the areas I suggest later) will be likely seen as superfluous. Finally, Disney and most theme parks are leaning heavily toward IP (intellectual property) supporting most expansions. Almost all of Disney's announced future plans center in some way around Disney-owned intellectual property. When Disney does decide to invest significantly in Animal Kingdom again, I would imagine any new land or attraction will have some significant tie to an intellectual property, whether Indiana Jones or something else. Any animals added will likely be those which can fit in with the IP.
Having said all that, many true Disney fans believe Animal Kingdom is the crown jewel of Disney World parks in terms of design, and Disney appears to recognize this in its careful attention to detail (the oft-maligned Pandora expansion fits the (until recently) undersung portion of Animal Kingdom's original intention to focus on real, prehistoric, and mythical creatures). It is worth noting that while Pandora is, of course, IP focused (as is the soon-to-open reimagined bird show, which will tie into the movie Up), other recent additions (albeit of a much smaller scale), such as Rivers of Light and Tree of Life Awakenings, do not have a strong IP but instead rely on concepts developed from the ideas around which the park was originally conceived.
