Vega support on the Mac side likely won't arrive until the hardware starts shipping in the iMac Pro, expected in December. That gives them a bit of time to cook on the developer side before arrival.
The real Mac Pro replacement isn't going to arrive until well into 2018. I'm just pleased that we're getting a real update (NOT LIKE I HAVEN'T BEEN WAIT FOR MORE THAN HALF A DECADE) with real PCIe slots it seems.
Dual Opteron 6376, 96 GB DDR3, Asus KGPE-D16, GTX 970
Mac Pro Dual Xeon E5645, 48 GB DDR3, GTX 770
Core i7 3930K@4.2 Ghz, 32 GB DDR3, GA-X79-UP5-Wifi
Core i7 2600K@4.4 Ghz, 16 GB DDR3, GTX 970, GA-X68XP-UD4