you will rot away as an SO for more than half a decade
My view is that statements like this are overly pessimistic. When you look at the huge increase in aircraft numbers multiplied by the number of pilots required to fly them, then it is obvious that their will be massive career progression. I believe that all existing S/O's who want an F/O position will have one in less than three years and therefore those new hires who get in early will do their F/O upgrade after about three years on line. For International operations this is sufficient time to develop their airline experience and route knowledge prior to doing the upgrade training.
If pilots reject working for Jetstar Intl, then there would probably be even more aircraft flown by pilots that are on reasonable salaries and T & C's. The management would not allow J* aircraft to sit on the ground for lack of pilots.