I am sure it will not be long before we get an answer to this question. As for GPUs, any current card would work on the windows side and I believe only the current AMD cards will work on the mac side... I wouldn't stick anything more powerful in there then the 1060 and 470/480... Due to the bandwidth limitations of thunderbolt 3, a higher graphics card will be wasted in my opinion.
The razer core might not work but I would think that at least a generic pcie to thunderbolt 3 box would work for an eGPU. You just might not get the hot swapping ability and internal display support of the core.