It's not her UA costume though. This is Rogue's original costume which she always comes back to in pretty much every era. She wore this as part of the Brotherhood before defecting to the X-Men. Didn't come back to it until the late 90s during the Alan Davis run. Then wore it again in the return to AoA in the mid-2000s with a cloak, around the same time she wore a cloak version in the 616 universe when she was leading her own X-Men team. Then she wore a variation with a skirt in UA.