So.. Apple waited 3 years before giving thought to a serious Mac Pro update and now it's going to take another year, so 4 years for an update? I've waited long enough for the Mac Pro 7,1. I'm in the middle of investigating / picking parts for my Hackintosh project at half the price or less. And I'm not going to wait for another year.
If your apps run on Windows and you are building a PC, I'd just go for Windows. Windows 10 is great and you don't need to worry about it not being supported. #easylife