If it doesn't work out between her and her bf, then I think you should go for it if she feels the same way about you. It never would hurt to ask.

The downfall is that there is a big risk of losing the friendship you have. People always say they'll be your friend if things don't work out but truthfully the relationship is never the same as it once was. You see, you'll have that friendship, but also the feelings, resentments, etc. that you had in the relationship. And then one or the other may still have strong feelings for the other.

Like with my ex, we are still friends, but it's nothing near what it was. I'm still in love with her, and can get quite possessive at times and very jealous of her other relationships. We've both moved on in life but that doesn't mean I don't get overly jealous of the people she's interested in. Needless to say we are farther apart now than we ever were.