Macbook Pro retina 10,1 (GT650M) + Vega56 on macOS is possible?
I have that same laptop and a Vega56 in an Akitio Node working well under Mojave and Windows. OS X is easy - combination of PurgeNVDA and PurgeWrangler. Windows 10 was a PITA - had to re-install the whole thing from scratch not using boot camp to get it installed in UEFI mode not MBR mode.
I did have to upgrade the Power Supply of the Akitio Node though, the standard one would crash under heavy strain.