One last thing... I feel like rifts are sorta like side stories, and I enjoy them as such. As a game mechanic, they are like mini games or a side quest. Fun, but not the focus. As an author mechanic, I believe they work in a similar way, and mostly act as an emotional relief. Fun, but help transition us into the next part of the storyline. Personally, I would make the rifts into my playground. Anything goes, because it doesn't have to have any major impact on the main story.
Good luck!