The Real Housewives of New Yorkfans might want to wait before they celebrate Rebecca Minkoff joining the cast. Sources familiar with the situation tell RadarOnline.comthat while the controversial fashion designer has filmed with the ladies, her role has yet to be determined. We have confirmed that Minkoff — a longtime Scientologist — hasn’t been cast as an official housewife or been given any title yet. Unless things change, she won’t be holding a bright red apple alongside Sai De Silva, Ubah Hassan, Erin Lichy, Jenna Lyons, Jessel Taank, and Brynn Whitfield for Season 15. Insiders shared that…