MVC's blog announced that Sierra natively supports eGPU, no hackery or tricks required.
http://www.macvidcards.com/blog/macos-sierra-had-native-egpu-support
http://www.macvidcards.com/blog/macos-sierra-had-native-egpu-support
First attempt with one of our flashed Titan-Xs on nMP 6,1 showed some new info in the Displays panel about "automatic display switching". Perfect boot, display working, CUDA working. No system mods whatsoever.
Not sure how non-EFI cards will work.
Not sure how laptops will work.
But this is a HUGE step forward for OSX !