Installation was straight forward. Update Windows and Thunderbolt 3 Drivers > Plug in Razer Core X > Install AMD Adrenalin Drivers > Restart PC > Plug Into External monitor > Done.
I am extremely happy with the performance of both the XPS 13 and the Vega 64. While the XPS 13 boosts very hard when initially under load, often rocketing virtually instantly to 4.5Ghz and 100'C, it will stabilize and sit at constant 3.00Ghz with an average temperature of under 70'C. This is a great improvement over the S730, which did not hit as high of a boost clock, and sat at approximately 2.00Ghz average CPU Core Clock with a very similar temperature.
The attached Unigine Heaven benchmark scored essentially the same as my overclocked 1070 eGPU setup did, but I believe this is because of Unigine only being a DX11 program. AMD Vega cards perform better in DX12 titles, as well as in higher resolution.
After a couple of issues with my Lenovo S730 eGPU setup across three different graphics cards, I decided to purchase a new laptop in the hope of establishing a 'perfect' eGPU setup, with the stability and performance of the desktops I used to own, and Dell seems to have done it. The XPS 13 works absolutely flawlessly, without any issues. Can happily leave the eGPU plugged in permanently, with no problems restarting, shutting down, booting up or using games and applications.
For reference, I re-pasted both the Dell XPS 13 9380 and the AMD RX Vega 64 with Thermal Grizzly Kryonaut, and also added a 1mm thick thermal pad to a portion of the XPS's heatsink, which creates a thermal pathway to the aluminum underside.
Sorry for the late reply! It appears you found a fix for it which is great. I am running 1903.
The only problem I ever ran into with the XPS was if I did a hard shutdown or unplugged the eGPU, it would recognise it but not have enough resources to run it. I fixed this by using Device Manager to disable it, then shutting down the laptop with it plugged it, then turning it back on, re-enabling it which then prompted a restart, restarting it and it would work fine.