Have 12 core 2012 Mac Pro. Install of Sierra went fine until I noticed no wifi connection. Airport says "no hardware". Could not find a way to work around it including resetting PRAM and deleting wifi and networking preferences. Still reporting "no hardware". Solution: Erased Sierra disk and began re-install of El Capitan from TM BU. Immediately, wifi is alive and well. So this is a Sierra bug, no hardware issue. Installed Sierra on I7 13" MBA, 2015, with no issues. Will hold off on other desktop installs until the bug is cleared because who has 8 hours to waste on each install?
OS X El Capitan (10.11), 2008 Mac Pro 8 core
