The role of the Ethnomusicologists as a whole (Wanda Bryant being one of them) in the film and its musical reflections also plays a vital key roll in the musical expression of the world of Avatar I hope she is back for the sequels and you can hear her interview , Avatars unique sound space expression owes a lot to work in this Area

https://youtu.be/9WI3kJIObHE

Just going to toss the name Klaus Badelt into this thread .

I think Steve Jablonsky would be an excellent successor to James Horner for the Avatar sequels. He has created very memorable scores, especially when it comes to the Transformers film series. The one thing that stands out in them is the vocalizing. It is very beautiful and haunting. Since Lisbeth Scott did vocals for the first film, she could team up with James Cameron once again as well as reunite with Steve due to her participation as a vocalist for Transformers: Revenge of the Fallen.

i hope there is still unpublished James Horner music that can be incorporated into the sequel, as well as being augmented by the new composer.

I really hope they use some of the original scores in the future films...