RX Vega cards are supported, they are not as fast in gaming or with windows apps but MacOS apps run well on them. High Sierra and Mojave has native support so no need for web drivers. If you only need it for Mac it’s a good choice.
Vega 64 is a very fast GPU, especially in compute operations like OpenCL etc.
For games, it's not as good as a 1080Ti, it sits between the 1070 and 1080 and sometimes trades blows with the 1080 in some optimized games.
But other than that, it is an excellent GPU for pro apps like Davinci Resolve, Premiere, FCPX etc.
Anyone who REALLY wants to get a 2080Ti, I recommend you go with a Vega 64 and then when drivers are out sell it and buy a 2080Ti....
But I may be the only one who brings this up, but is it really worth paying $1200+ for a GPU that will not really help you in professional work? It's only really good if you are a gamer and want to get 60fps at 4k. Anyone who's interested in realtime Raytracing, prepare to only get 1920x1080 @ 30fps with these cards as they are 1st gen RTX cards. You have to turn it off if you want to play games at higher resolutions and framerates. It's just not ready for prime-time, but it's a great start for what it is.
Honestly if you NEED CUDA, stick to Windows. You may be doing some heavy lifting if you need that many CUDA cores...