I would like to second this as I did the Phase One Certified Professional training and was told by a few of the higher up Phase One staff that the new Dalsa chips are unable to handle the longer exposures in the IQ backs, and it is most likely not going to happen considering the cease of use for the Kodak chips in the P45+I wouldn't hold your breath for the IQ version of a P45+. When I spoke with the development manager of the IQ series he was at pains to point out their inability to do this without a new source of sensors and the lack of such source. He was a straight-up engineer/manager who looked me straight in the eye without any marketing BS so I tend to believe him. (Either that or one heck of a poker player)
I would have loved a long exposure back with the IQ features.