You mean not confirmed for 10.13?Yes the Akitio Thunder 2 works with the RX 580 in 10.13.
Nvidia cards not yet confirmed to run natively.
However, up to macOS 10.12.x you can use Nvidia cards: https://egpu.io/setup-guide-external-graphics-card-mac/
So, I could buy a 8Gb 580 for around £310 plus a Akitio Thunder2 for £260, plug it into my late 2015 27” iMac and I’d be good to go?
Hmmm... maybe you're right!asfik this only works to drive an external display, not the iMacs retina screen