Not sure how Des will use him. I used to love him as an edge forward but with his injuries now for basically two years (I am sure he played injured last year) I have no idea about his mobility to play an edge - time will tellI think you might be right.
What will be interesting is whether Siro will now be used as a middle forward or on an edge. I would suggest that his days as an edge might be over and he is used for some direct running with quick play-the-balls and to help Jake tighten up our defence in the middle. This is the way I would use him if he makes the 17.