Mostly posting this so others will be aware. I recently purchased all of the same equipment that Apple is selling as their eGPU VR Developer Kit. A Sonnet eGFX breakaway box and AMD RX580 GPU. I have hooked these up to my 2016 MacBook Pro and they work as expected. Nearly anything run from the external monitor hooked into the eGPU directly is accelerated by the eGPU and not the internal.
I bought this as a test unit (I knew that it wasn’t officially supported) to see if I could offload the GPU work from mimoLive to the eGPU to reduce internal (to the laptop) heat load to prevent thermal throttling after long stream sessions and possibly to get a little performance boost as well since the RX580 is significantly more powerful than the internal Radeon Pro 460. Unfortunately, at this time mimoLive does not appear to be offloading the GPU work load to the eGPU even after tinkering with various setups and settings in the Debug menu, running mimoLive from the external monitor, and setting the external monitor as the primary display.
I will attempt to keep this space updated as I work through this with the Boinx devs.