Its just a rumor on 'Mac Rumors' but they speculate that Apple is not going to support the Mini any longer and their plan to let it die, or (phase it out) in the not to distant future.
Hence we see no love or attention given to the Mini since its last update back in 2014.
Sad I know but it seems that Apple is more enamored with the IPhone line (read mega profits) then any of the basic items that kept them together in the very beginning.