Apple is reportedly deliberately reducing current iMac shipments which, if true, could be an indication that new iMac updates are a few weeks away.
Both the iMac and Mac Pro lines are in need of a refresh, and desktop sales for Macs are beginning to sag slightly, so updated internals on both lines would not be surprising in the near future.
Don’t, however, expect a complete model redesign of either product. Out of the two, the Mac Pro is the most likely to receive a case refresh, but there is nothing seriously pointing in that direction at this time.