Production Weekly [1] posted a cryptic tweet announcing James Cameron is in development on a new sci-fi event film. The new production will be scripted by Shane Salerno. The Fox project is mostly likely DOOMSDAY PROTOCOL, which Cameron previously announced he was working on. Cameron would be the producer only. The story follows a group of humans and aliens that come together to save Earth.
Links:
[1] http://twitter.com/prodweek/status/6488770534