It was either sequels or a reboot.
Cameron Talks AVATAR Sequel - Mania.com
"I've had a storyline in mind from the start - there are even scenes in 'Avatar' that I kept in because they lead to the sequel," Cameron said. "It just makes sense to think of it as a two or three film arc, in terms of the business plan. The CG plants and trees and creatures and the musculo-skeletal rigging of the main characters — that all takes an enormous amount of time to create. It'd be a waste not to use it again."