In the newly released macOS High Sierra 10.13.4 update, Apple computers will now be able to take advantage of external graphics solutions. MacBook Pro models from 2016 or later and iMacs from 2017 and beyond can now make use of eGPUs once the latest update is installed.
Apple is officially supporting graphics cards based on AMD's Polaris architecture. That includes the RX 570, RX 580, Radeon Pro WX 7100, RX Vega 56, RX Vega 64, Radeon Pro WX 9100 and Vega Frontier Edition graphics cards. Hardware acceleration using Metal, OpenCL and OpenGL is now possible using an external graphics enclosure.
For those curious about whether Nvidia is being left out in the cold, they are. There is no official support for Nvidia graphics cards at the current time. However, there were beta drivers released for 10-series Pascal cards last year, so future support seems somewhat likely.
All supported graphics card enclosures make use of Thunderbolt 3 and must provide 85W of power to charge MacBook laptops while also supplying adequate power to the GPU. On 13-inch MacBook Pro models, the left-hand ports must be used for best performance.
External graphics support should be a welcome addition for Final Cut Pro users. Since Final Cut now supports virtual reality headsets, significantly better hardware is required to view and modify 360-degree video. For non-video editors, the ability to add more external displays capable of higher refresh rates could be beneficial.
Along with the introduction of eGPU support, Apple has published a fairly comprehensive collection of documentation for developers. Everything from determining which GPU is currently driving the user's display to transferring data between multiple graphics cards is well outlined. There should be little in the way of software development going forwards.