If I'm not mistaken there's only one or two IMAX theaters that still uses film prints. The IMAX I typically go to is full size but they went digital about a year ago. The last film I saw there was TDKR. Ever since then it's been digital projection when I've gone. Seeing STID was a bit of a disappointment, as the IMAX weren't full size and didn't seem to be of much higher quality.
Can the DCP produce the same image quality as the 70mm? I doubt it, but would like to hear an exact answer. Nolan's filming more in IMAX for Interstellar than anyone has ever done before, and I'd like to know if, when I see it, it will be full quality.