The realities of digital VFX production heavy movies make an extended cut (unless it is planned for from the beginning) unlikely. Usually as soon as a shot is dropped from the cut, work on it is being stopped immediately. The only reason we got to see some stills of the CG creature of the Fifield attack is that apparently the decision to go for the practical one was made rather late.
Usually in the facilities, since disk space is always an issue, things get archived soon after the project is completed. So while it is perfectly possible to go back to the archives and finish shots that were dropped early on, it happens rarely.
So, if we do see an extended cut, it would most likely only envolve less vfx heavy, dialogue scenes...