I would image it would be rated 'M' like the previous entry in the series. If you watch some gameplay footage from Prey 2 (like this: http://www.youtube.com/watch?v=dNsVodE1yS0), you'll see it features violence, including dismemberment, and foul language. Sure signs that they would be aiming for a mature rating.
However, it's very doubtful the game is even being worked on at all. I would be surprised if it hasn't been left to languish in the same state for over a year, if not outright cancelled.