I don't care about today's technique standards. The home theater version of Avatar 2 will be released in ... more than 4 years? For years ago I used to watch DVDs. BluRay is the new standard and it's yet some years old. The second and third movie will be published with a new standard, maybe even the generation after the next generation, who really knows?
And if not, releases n a higher quality are possible everytime in the future. The only requirement is original material in the best possible quality.
So Cameron should produce the movie in the best quality and because he's a technophile person I know that he'll do.
One day there will be TVs and data storages in 4K, 100 and more FPS are already given by every TV you can buy.