Smoking in internal codes from the latest version of OS X El Capitan, the Pike?s Universum discovered references to a possible new model of the Mac pro identified as AAPLJ951.1 (the current AAPLJ901.1).
Due to the similarity of the codes, it is quite possible that we are talking about a MacPro7.1 then an evolution of MacPro6.1 released at the end of 2013. There is no concrete rumor yet about it, but it is quite capable that this is a general update of internal components ( including new generation Intel Xeon chips Broadwell) without external visual changes.
A curious part of the codes found that they indicate the presence of ten (!) USB 3.0 ports, while the current model has only four. But honestly, I doubt very much that we see this happening in practice.
There is still time for this new Mac Pro to come out this year or maybe in early 2016