As far as I understand the way to have scaling UI in Urho is to use the automatic layout modes.
But it isn’t possible to have elements that maintain their aspect ratio, for example icon images.
Aspect ratio is relative to the height or width of the parent, this way it can work with the layout modes.
Parent needs to be in free layout mode so the element can be resized? (or maybe implement horizontal/vertical aspect ratio as a new layout modes, if that makes sense?)
Having the font size relative to its parent’s height (similar to aspect ratio) is also needed to have scaling UI.
With both aspect ratio and font size relative to parent, I think it would be possible to make fully scaling UI layouts.