a Rob/Rae story I think it could be cool if it is a BB/Star story too. That would really make it pretty unique. If she does choose Robin the she could say she does love BB but as a brother.
Then BB may be a bit sad at first then find out later that Star is and has been interested in BB for quite a while but didn't say anything because she thought Raven and BB were going to be together and didn't want to get in the way of their potential relationship. Now that Star knows she would not be hurting Raven she my make a move on BB.