I often work with importing and rendering architect models coming from Revit, and more often than not, they are a complete mess when it comes to materials. Being able to render Autodesk Materials would help immensely - it wouldn't even have to be a perfect representation of the original material - just make it so it doesn't render that red warning material!
Alternatively, provide the option to override non renderable materials with a corona material of your choice Like the "Mtl. override" we have now, but with the added option to only replace the problem materials.
Also, a side note: It would be very useful to be able to ignore material warnings in the render all together. Thinking primarily of the message you get if you have an undefined distance texture.
I don't need it to screw up my render; a note in the Error Message log is more than enough.
Cheers!