I've recently discovered the beauty that is using substance designer to create UI elements. Have many people tried this? Especially with the new text node, I don't think I'll ever need Photoshop again. The nondestructive workflow is a massive boom for this type of work. Now of course, I could see issues if you needed to…
I use it myself to create buttons and widgets sometimes that I then use in UE4. As you mention, the non-destructive workflow is perfect for that, especially for iterating on color and adding quick effects. :) You can even try to bake lighting information by using a normal map and the light node, etc.