That is of course the most obvious solution. However, I often just need to output something very quickly, and then later go back and set the materials properly. Having converted the materials isn't always the most practical thing in those cases.
Also, we work a lot with linked FBX models, and then do an "Xref Scene" into the scene where we have cameras, lights and other additions. In these cases I have to open the linked scene, edit the materials and reload the model in my render scene. A bit cumbersome, and therefore having the feature I requested would help.
I just thought I should give some further insight to the problem. When working with Revit, you get these pesky unsupported materials. What I do is that I have a matlib which replaces the revit materials. This works as long as the architects stick to the default materials, but ever so often, they import some 3rd party geometry, which has new materials. When updating, they slip through unnoticed - until you render. So, having a possibility to just override all unsupported materials would be great.