I heard that the upcoming game myst 5 will use a version of the Havok engine in it. But I also heard that legal problems prevent Havok to be released for the mac platform. This is the cause of other games not being ported (Half Life 2). I hope you prove me wrong... I really liked all the other Myst games.
Last I saw This is the last article I saw on it. Seems like a mac confirmation to me. http://www.insidemacgames.com/news/story.php?ArticleID=11572
Cyan vowed never to touch Havok again after what happened with Uru. Apparently Havok told them that it was a cross-platform API, so they used it. Imagine how annoyed/angry they would've been when they discovered they'd been lied to