4,1 isn't compatible with Sierra out of the box. Will 5,1 suffer the same fate next year? I'd think it likely were it not for the minor revision the 5,1 series received in 2012, nearly identical to the 2010 models. Or would Apple abandon the 2010 Mac Pro and support the 2012s?* * That said, is there a way to make a 2010 appear to be a 2012 to macOS?