Fox has shuffled a bunch of their release dates include bumping Alien: Covenant forward from August to May of next year.
Another interesting date the studio has mapped-out is December 21st, 2018 for a James Cameron Project. This is very unlikely being set aside for Alita: Battle Angel, as it’s already begun production back in October and has a set release date of July 20th, 2018. There had been plans originally to make an Alita trilogy, but it’s doubtful we’ll see a sequel released a couple months after Battle Angel.
Avatar came out during the holiday season and we’d expect to see production on it’s sequel to begin sometime in 2017. Returning actress Sigourney Weaver has repeatedly stated the Avatar sequels have delayed production on Neill Blomkamp’s Alien 5.
While I believe we’ll end-up seeing James Cameron acting as an executive producer on Alien 5, due to it being a direct sequel to his film Aliens and publicly approving of Blomkamp’s script. The film is a couple of years away from getting the green light due to Alien: Covenant bumping it.
In all likelihood, the project that makes the most sense at the moment looks to be Avatar 2, as it’s about to start production very soon.