Considering that highest end iMac best all but the highest end Mac Pros, its a safe bet that the Mac Pro is due for an upgrade. Pike’s Universum found evidence of a likely new Mac Pro model with 10 USB 3.0 ports

Call me a cynic, but if the hypothetical Mac Pro returned to one with 4 PCIe slots, one could add as many USB 3.0 ports as one so desire.