> on AMD you might get to the point where the lowest iGPU shares
> it's architecture with some discrete Radeon already supported.

Currently with newest supported GPU architecture being TeraScale 2, this would be AMD SoCs from 2011:

https://en.wikipedia.org/wiki/List_of_AMD_processors_with_3D_graphics#Lynx:_%22Llano%22_(2011)
https://en.wikipedia.org/wiki/List_of_AMD_processors_with_3D_graphics#Sabine:_%22Llano%22_(2011)
https://en.wikipedia.org/wiki/List_of_AMD_processors_with_3D_graphics#Brazos:_%22Desna%22,_%22Ontario%22,_%22Zacate%22_(2011)
https://en.wikipedia.org/wiki/List_of_AMD_processors_with_3D_graphics#Brazos:_%22Ontario%22_and_%22Zacate%22_(2011)