Imho a new Pro/high end iMac will be all about how sales go over the next 18 months with Apple’s new wider Mac line up. If rumors hold true we will see an upgraded Mac mini, MBA or 13” MB Pro by Christmas. Apple is putting low, mid and high end laptops and desktops out there plus the 24” IMac. That appears to be well shaped for the market. Ultimately I suspect Apple would have to see a specific sales category slump out of this wide Mac lineup before putting out a high end iMac.